Mass spectrometer

ABSTRACT

A mass spectrometer is disclosed comprising a first quadrupole rod set mass filter, a collision cell, an ion mobility spectrometer or separator, an ion guide or collision cell arranged downstream of the ion mobility spectrometer or separator, a second quadrupole rod set mass filter and an ion detector.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.11/720,771 filed Dec. 29, 2009, which is the National Stage ofInternational Application No. PCT/GB2005/004672, filed Dec. 7, 2005,which claims benefit of and priority to U.S. Provisional PatentApplication No. 60/637,835, filed on Dec. 21, 2004 and United KingdomApplication No. 0510914.5 which was filed on and May 27, 2005 and UnitedKingdom Application No. 0426778.7 which was filed on and Dec. 7, 2004.The contents of these applications are expressly incorporated herein byreference in their entirety.

BACKGROUND OF THE INVENTION

The present invention relates to a mass spectrometer and a method ofmass spectrometry.

Tandem mass spectrometry, or MS/MS, has become the preferred technologyfor many applications in which mass spectrometry plays a part. Tandemmass spectrometry allows selection and isolation of specific compoundsof interest and their subsequent identification. The extra selectivityof MS/MS enables this technology to be used for quantification of targetcompounds even in the presence of complex matrices.

Tandem mass spectrometers are known which comprise a mass filter, acollision cell arranged downstream of the mass filter which fragmentsselected parent or precursor ions, and a mass analyser which massanalyses the fragment or daughter ions which emerge from the collisioncell. Ions are fragmented in the collision cell by Collision InducedDecomposition (“CID”) wherein ions undergo multiple collisions with gasmolecules in the partially enclosed collision cell.

In most tandem mass spectrometers the processes of selecting specificparent or precursor ions, fragmenting the selected parent or precursorions and mass analysing the resulting fragment or daughter ions takesplace sequentially in space. The mass filter may be used to selectparent or precursor ions of a target compound. The parent or precursorions are then passed to a collision cell which fragments those parent orprecursor ions. The mass analyser is then used to mass analyse theresulting fragment or daughter ions.

One known tandem mass spectrometer is commonly referred to as a triplequadrupole mass spectrometer. Triple quadrupole mass spectrometerscomprise a first quadrupole rod set mass filter or mass analyserfollowed by a collision cell. A second quadrupole rod set mass filter ormass analyser is arranged downstream of the collision cell followed byan ion detector. The name triple quadrupole is derived from the firstsuch instrument wherein an RF quadrupole was used to guide ions throughthe collision cell.

The first quadrupole rod set mass filter is typically used to selectparent or precursor ions having a specific mass to charge ratio.Therefore, in order to record a full mass spectrum, the first quadrupolerod set mass filter must be scanned across the full mass to charge ratiorange in order to sequentially transmit ions having different mass tocharge ratios. The duty cycle for this process is relatively low and asa consequence the sensitivity of a quadrupole rod set mass filter whenused to record a full mass spectrum is relatively poor. On the otherhand, the quadrupole mass filter will have 100% duty cycle when used totransmit ions having a specific mass to charge ratio.

A triple quadrupole mass spectrometer may be used for Selected ReactionMonitoring (“SRM”) experiments wherein parent or precursor ions having aspecific mass to charge ratio are arranged to be transmitted by thefirst quadrupole rod set mass filter arranged upstream of the collisioncell. The specific parent or precursor ions are then transmitted to thecollision cell and are fragmented thereby forming fragment or daughterions. The second mass filter is arranged so as to transmit fragment ordaughter ions having a specific mass to charge ratio. This arrangementis very specific and exceptionally sensitive. Triple quadrupole massspectrometers have found significant use in the drug discovery anddevelopment process where they are used both for Selected ReactionMonitoring experiments and also for Multiple Reaction Monitoring (“MRM”)experiments to quantify target compounds of biological significance.

A limitation of conventional triple quadrupole mass spectrometersbecomes evident when a conventional mass spectrometer is attempted to beused in a Multiple Reaction Monitoring (MRM) mode to monitor manydifferent transitions or reactions. For each additional reaction that isincluded in an experiment, there is a corresponding reduction in thesampling duty cycle for each reaction monitored. For confirmation orvalidation of certain quantification analyses it is desirable to monitorseveral reactions. Indeed, for some applications it is a regulatoryrequirement to monitor several reactions in order to confirm or validatethe quantification analysis.

A common application in peptide and protein analysis for a triplequadrupole mass spectrometer makes use of a parent or precursor ionscanning mode of operation. In this mode of operation the second massfilter or mass analyser arranged downstream of the collision cell is setso as to transmit only a specific characteristic fragment or daughterion. The first mass filter arranged upstream of the collision cell isscanned so as to sequentially transmit different parent or precursorions to the collision cell for subsequent fragmentation. When a specificfragment or daughter ion is detected then the mass to charge ratio ofthe corresponding parent or precursor ions which were transmitted by thefirst mass filter upstream of the collision cell are recorded. Thisapproach has proved particularly useful in the analysis of proteinpost-translational modifications such as phosphorylation andglycosylation. However, since it is necessary to scan the firstquadrupole mass filter upstream of the collision cell then the samplingduty cycle can be quite low, commonly less than 1%, and consequently thesensitivity is also relatively low.

It is therefore desired to provide an improved mass spectrometer andmethod of mass spectrometry which does not suffer from some or all ofthe disadvantages of the prior art.

SUMMARY OF THE INVENTION

According to an aspect of the present invention there is provided a massspectrometer comprising:

a first ion guide or a first collision, fragmentation or reaction devicearranged and adapted to fragment or react ions and to produce product,daughter, adduct or fragment ions; and

an ion mobility spectrometer or separator arranged downstream of thefirst ion guide or the first collision, fragmentation or reactiondevice, the ion mobility spectrometer or separator being arranged totemporally separate product, daughter, adduct or fragment ions accordingto their ion mobility which emerge from or which have been transmittedfrom the first ion guide or the first collision, fragmentation orreaction device.

Ions are preferably fragmented or reacted in the collision fragmentationor reaction device and the resulting fragment, daughter, product oradduct ions are then preferably temporally separated in an ion mobilityspectrometer or separator and are preferably detected by an iondetector.

According to an embodiment the collision, fragmentation or reactiondevice may be arranged and adapted to fragment ions by Collision InducedDissociation (“CID”). According to this embodiment, ions may beaccelerated such that they have a relatively high kinetic energy whenthey enter the device that they are caused to fragment into fragment ordaughter ions upon colliding with gas molecules in the device.Alternatively and/or additionally, ions may accelerated within thedevice such that they collide energetically with background gasmolecules within the device and fragment into fragment or daughter ions.

Alternatively, the collision, fragmentation or reaction device mayselected from the group consisting of: (i) a Surface InducedDissociation (“SID”) fragmentation device; (ii) an Electron TransferDissociation fragmentation device; (iii) an Electron CaptureDissociation fragmentation device; (iv) an Electron Collision or ImpactDissociation fragmentation device; (v) a Photo Induced Dissociation(“PID”) fragmentation device; (vi) a Laser Induced Dissociationfragmentation device; (vii) an infrared radiation induced dissociationdevice; (viii) an ultraviolet radiation induced dissociation device;(ix) a nozzle-skimmer interface fragmentation device; (x) an in-sourcefragmentation device; (xi) an ion-source Collision Induced Dissociationfragmentation device; (xii) a thermal or temperature sourcefragmentation device; (xiii) an electric field induced fragmentationdevice; (xiv) a magnetic field induced fragmentation device; (xv) anenzyme digestion or enzyme degradation fragmentation device; (xvi) anion-ion reaction fragmentation device; (xvii) an ion-molecule reactionfragmentation device; (xviii) an ion-atom reaction fragmentation device;(xix) an ion-metastable ion reaction fragmentation device; (xx) anion-metastable molecule reaction fragmentation device; (xxi) anion-metastable atom reaction fragmentation device; (xxii) an ion-ionreaction device for reacting ions to form adduct or product ions;(xxiii) an ion-molecule reaction device for reacting ions to form adductor product ions; (xxiv) an ion-atom reaction device for reacting ions toform adduct or product ions; (xxv) an ion-metastable ion reaction devicefor reacting ions to form adduct or product ions; (xxvi) anion-metastable molecule reaction device for reacting ions to form adductor product ions; and (xxvii) an ion-metastable atom reaction device forreacting ions to form adduct or product ions.

A reaction device should be understood as comprising a device whereinions, atoms or molecules are rearranged or reacted so as to form a newspecies of ion, atom or molecule. An X-Y reaction fragmentation deviceshould be understood as meaning a device wherein X and Y combine to forma product which then fragments. This is different to a fragmentationdevice per se wherein ions may be caused to fragment without firstforming a product. An X-Y reaction device should be understood asmeaning a device wherein X and Y combine to form a product and whereinthe product does not necessarily then fragment.

The collision, fragmentation or reaction device may be arranged andadapted to trap ions within the collision, fragmentation or reactiondevice in a mode of operation.

According to an embodiment the collision, fragmentation or reactiondevice is arranged and adapted to pulse ions out of the collision,fragmentation or reaction device and into or towards the ion mobilityspectrometer or separator.

The mass spectrometer preferably further comprises a mass filter or massanalyser arranged upstream and/or downstream of the first ion guide orthe first collision, fragmentation or reaction device. The mass filteror mass analyser is preferably selected from the group consisting of:(i) a quadrupole rod set mass filter or analyser; (ii) a Time of Flightmass filter or mass analyser; (iii) a Wein filter; and (iv) a magneticsector mass filter or mass analyser.

According to another aspect of the present invention there is provided amass spectrometer comprising:

a first mass filter or mass analyser;

an ion mobility spectrometer or separator, the ion mobility spectrometeror separator being arranged downstream of the first mass filter or massanalyser; and

a second mass filter or mass analyser arranged downstream of the ionmobility spectrometer or separator.

The first mass filter or mass analyser and/or the second mass filter ormass analyser is preferably selected from the group consisting of: (i) aquadrupole rod set mass filter or analyser; (ii) a Time of Flight massfilter or mass analyser; (iii) a Wein filter; and (iv) a magnetic sectormass filter or analyser.

The first mass filter or mass analyser and/or the second mass filter ormass analyser preferably comprises a plurality of electrodes or rods. Ina first mode of operation substantially all of the electrodes or rods ofthe first mass filter or mass analyser and/or the second mass filter ormass analyser may be maintained at substantially the same DC potentialor voltage.

In the first mode of operation the first mass filter or mass analyserand/or the second mass filter or mass analyser is preferably operated ina substantially non-resolving or ion guiding mode of operation.

In a second mode of operation adjacent electrodes or rods of the firstmass filter or mass analyser and/or the second mass filter or massanalyser are preferably maintained at substantially different DCpotentials or voltages. In the second mode of operation a DC potentialor voltage difference is maintained between adjacent electrodes or rodsof the first mass filter or mass analyser and/or the second mass filteror mass analyser, wherein the DC potential or voltage difference ispreferably selected from the group consisting of: (i) <1 V; (ii) 1-2 V;(iii) 2-3 V; (iv) 3-4 V; (v) 4-5 V; (vi) 5-6 V; (vii) 6-7 V; (viii) 7-8V; (ix) 8-9 V; (x) 9-10 V; (xi) 10-20 V; (xii) 20-30 V; (xiii) 30-40 V;(xiv) 40-50 V; (xv) 50-60 V; (xvi) 60-70 V; (xvii) 70-80 V; (xviii)80-90 V; (xix) 90-100 V; and (xx) >100 V. In the second mode ofoperation opposed electrodes or rods of the first mass filter or massanalyser and/or the second mass filter or mass analyser are preferablymaintained at substantially the same DC potential or voltage.

In a mode of operation the first mass filter or mass analyser and/or thesecond mass filter or mass analyser is preferably operated in aresolving or mass filtering mode of operation.

In a mode of operation the first mass filter or mass analyser and/or thesecond mass filter or mass analyser is preferably scanned.

In a mode of operation the first mass filter or mass analyser and/or thesecond mass filter or mass analyser is preferably scanned in synchronismwith the ion mobility spectrometer or separator.

In a mode of operation the first mass filter or mass analyser is scannedin synchronism with the second mass filter or mass analyser.

According to an embodiment the mass spectrometer preferably furthercomprises a first ion guide or a first collision, fragmentation orreaction device, wherein the first ion guide or the first collision,fragmentation or reaction device is arranged upstream of the ionmobility spectrometer or separator and/or downstream of the first massfilter or mass analyser.

The first collision, fragmentation or reaction device is preferablyarranged and adapted to fragment ions by Collision Induced Dissociation(“CID”).

Alternatively, the first collision, fragmentation or reaction device isselected from the group consisting of: (i) a Surface InducedDissociation (“SID”) fragmentation device; (ii) an Electron TransferDissociation fragmentation device; (iii) an Electron CaptureDissociation fragmentation device; (iv) an Electron Collision or ImpactDissociation fragmentation device; (v) a Photo Induced Dissociation(“PID”) fragmentation device; (vi) a Laser Induced Dissociationfragmentation device; (vii) an infrared radiation induced dissociationdevice; (viii) an ultraviolet radiation induced dissociation device;(ix) a nozzle-skimmer interface fragmentation device; (x) an in-sourcefragmentation device; (xi) an ion-source Collision Induced Dissociationfragmentation device; (xii) a thermal or temperature sourcefragmentation device; (xiii) an electric field induced fragmentationdevice; (xiv) a magnetic field induced fragmentation device; (xv) anenzyme digestion or enzyme degradation fragmentation device; (xvi) anion-ion reaction fragmentation device; (xvii) an ion-molecule reactionfragmentation device; (xviii) an ion-atom reaction fragmentation device;(xix) an ion-metastable ion reaction fragmentation device; (xx) anion-metastable molecule reaction fragmentation device; (xxi) anion-metastable atom reaction fragmentation device; (xxii) an ion-ionreaction device for reacting ions to form adduct or product ions;(xxiii) an ion-molecule reaction device for reacting ions to form adductor product ions; (xxiv) an ion-atom reaction device for reacting ions toform adduct or product ions; (xxv) an ion-metastable ion reaction devicefor reacting ions to form adduct or product ions; (xxvi) anion-metastable molecule reaction device for reacting ions to form adductor product ions; and (xxvii) an ion-metastable atom reaction device forreacting ions to form adduct or product ions.

The first ion guide or the first collision, fragmentation or reactiondevice preferably comprises:

(i) a multipole rod set or a segmented multipole rod set;

(ii) an ion tunnel or ion funnel; or

(iii) a stack or array of planar, plate or mesh electrodes.

The multipole rod set preferably comprises a quadrupole rod set, ahexapole rod set, an octapole rod set or a rod set comprising more thaneight rods.

The ion tunnel or ion funnel preferably comprises a plurality ofelectrodes or at least 2, 5, 10, 20, 30, 40, 50, 60, 70, 80, 90 or 100electrodes having apertures through which ions are transmitted in use,wherein at least 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%,60%, 65%, 70%, 75%, 80%, 85%, 90%, 95% or 100% of the electrodes haveapertures which are of substantially the same size or area or which haveapertures which become progressively larger and/or smaller in size or inarea. Preferably, at least 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%,50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95% or 100% of theelectrodes have internal diameters or dimensions selected from the groupconsisting of: (i) ≦1.0 mm; (ii) ≦2.0 mm; (iii) ≦3.0 mm; (iv) ≦4.0 mm;(v) ≦5.0 mm; (vi) ≦6.0 mm; (vii) ≦7.0 mm; (viii) ≦8.0 mm; (ix) ≦9.0 mm;(x) ≦10.0 mm; and (xi) >10.0 mm.

The stack or array of planar, plate or mesh electrodes preferablycomprises a plurality or at least 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12,13, 14, 15, 16, 17, 18, 19 or 20 planar, plate or mesh electrodesarranged generally in the plane in which ions travel in use, wherein atleast 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%,70%, 75%, 80%, 85%, 90%, 95% or 100% of the planar, plate or meshelectrodes are arranged generally in the plane in which ions travel inuse.

The mass spectrometer preferably further comprises AC or RF voltagemeans for supplying the plurality of planar, plate or mesh electrodeswith an AC or RF voltage and wherein adjacent planar, plate or meshelectrodes are preferably supplied with opposite phases of the AC or RFvoltage.

The first ion guide or the first collision, fragmentation or reactiondevice preferably comprises a plurality of axial segments or at least 5,10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95or 100 axial segments.

According to an embodiment the mass spectrometer preferably furthercomprises transient DC voltage means arranged and adapted to apply oneor more transient DC voltages or potentials or one or more transient DCvoltage or potential waveforms to electrodes forming the first ion guideor the first collision, fragmentation or reaction device in order tourge at least some ions along at least 5%, 10%, 15%, 20%, 25%, 30%, 35%,40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95% or 100% ofthe axial length of the first ion guide or the first collision,fragmentation or reaction device.

According to another embodiment the mass spectrometer preferably furthercomprises AC or RF voltage means arranged and adapted to apply two ormore phase-shifted AC or RF voltages to electrodes forming the first ionguide or the first collision, fragmentation or reaction device in orderto urge at least some ions along at least 5%, 10%, 15%, 20%, 25%, 30%,35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95% or 100%of the axial length of the first ion guide or the first collision,fragmentation or reaction device.

According to an embodiment the first ion guide or the first collision,fragmentation or reaction device has an axial length selected from thegroup consisting of: (i) <20 mm; (ii) 20-40 mm; (iii) 40-60 mm; (iv)60-80 mm; (v) 80-100 mm; (vi) 100-120 mm; (vii) 120-140 mm; (viii)140-160 mm; (ix) 160-180 mm; (x) 180-200 mm; (xi) 200-220 mm; (xii)220-240 mm; (xiii) 240-260 mm; (xiv) 260-280 mm; (xv) 280-300 mm; and(xvi) >300 mm.

The first ion guide or the first collision, fragmentation or reactiondevice preferably further comprises AC or RF voltage means arranged andadapted to apply an AC or RF voltage to at least 5%, 10%, 15%, 20%, 25%,30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95% or100% of the plurality of electrodes of the first ion guide or the firstcollision, fragmentation or reaction device in order to confine ionsradially within the first ion guide or the first collision,fragmentation or reaction device.

The AC or RF voltage means is preferably arranged and adapted to supplyan AC or RF voltage to the plurality of electrodes of the first ionguide or the first collision, fragmentation or reaction device having anamplitude selected from the group consisting of: (i) ≦50 V peak to peak;(ii) 50-100 V peak to peak; (iii) 100-150 V peak to peak; (iv) 150-200 Vpeak to peak; (v) 200-250 V peak to peak; (vi) 250-300 V peak to peak;(vii) 300-350 V peak to peak; (viii) 350-400 V peak to peak; (ix)400-450 V peak to peak; (x) 450-500 V peak to peak; and (xi) >500 V peakto peak.

According to an embodiment the AC or RF voltage means is preferablyarranged and adapted to supply an AC or RF voltage to the plurality ofelectrodes of the first ion guide or the first collision, fragmentationor reaction device having a frequency selected from the group consistingof: (i) <100 kHz; (ii) 100-200 kHz; (iii) 200-300 kHz; (iv) 300-400 kHz;(v) 400-500 kHz; (vi) 0.5-1.0 MHz; (vii) 1.0-1.5 MHz; (viii) 1.5-2.0MHz; (ix) 2.0-2.5 MHz; (x) 2.5-3.0 MHz; (xi) 3.0-3.5 MHz; (xii) 3.5-4.0MHz; (xiii) 4.0-4.5 MHz; (xiv) 4.5-5.0 MHz; (xv) 5.0-5.5 MHz; (xvi)5.5-6.0 MHz; (xvii) 6.0-6.5 MHz; (xviii) 6.5-7.0 MHz; (xix) 7.0-7.5 MHz;(xx) 7.5-8.0 MHz; (xxi) 8.0-8.5 MHz; (xxii) 8.5-9.0 MHz; (xxiii) 9.0-9.5MHz; (xxiv) 9.5-10.0 MHz; and (xxv) >10.0 MHz.

Preferably, singly charged ions having a mass to charge ratio in therange of 1-100, 100-200, 200-300, 300-400, 400-500, 500-600, 600-700,700-800, 800-900 or 900-1000 have a drift or transit time through thefirst ion guide or the first collision, fragmentation or reaction devicein the range: (i) 0-10 μs; (ii) 10-20 μs; (iii) 20-30 μs; (iv) 30-40 μs;(v) 40-50 μs; (vi) 50-60 μs; (vii) 60-70 μs; (viii) 70-80 μs; (ix) 80-90μs; (x) 90-100 μs; (xi) 100-110 μs; (xii) 110-120 μs; (xiii) 120-130 μs;(xiv) 130-140 μs; (xv) 140-150 μs; (xvi) 150-160 μs; (xvii) 160-170 μs;(xviii) 170-180 μs; (xix) 180-190 μs; (xx) 190-200 μs; (xxi) 200-210 μs;(xxii) 210-220 μs; (xxiii) 220-230 μs; (xxiv) 230-240 μs; (xxv) 240-250μs; (xxvi) 250-260 μs; (xxvii) 260-270 μs; (xxviii) 270-280 μs; (xxix)280-290 μs; (xxx) 290-300 μs; and (xxxi) >300 μs.

According to an embodiment the mass spectrometer preferably furthercomprises means arranged and adapted to maintain at least a portion ofthe first ion guide or the first collision, fragmentation or reactiondevice at a pressure selected from the group consisting of: (i) >0.0001mbar; (ii) >0.001 mbar; (iii) >0.01 mbar; (iv) >0.1 mbar; (v) >1 mbar;(vi) >10 mbar; (vii) 0.0001-0.1 mbar; and (viii) 0.001-0.01 mbar.

The mass spectrometer preferably further comprises first accelerationmeans arranged and adapted to accelerate ions into the first ion guideor the first collision, fragmentation or reaction device wherein in amode of operation at least 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%,50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95% or 100% of the ions arecaused to fragment or react upon entering the first ion guide or thefirst collision, fragmentation or reaction device.

The mass spectrometer preferably further comprises a control systemarranged and adapted to switch or repeatedly switch the potentialdifference through which ions pass prior to entering the first ion guideor the first collision, fragmentation or reaction device between arelatively high fragmentation or reaction mode of operation wherein ionsare substantially fragmented or reacted upon entering the first ionguide or the first collision, fragmentation or reaction device and arelatively low fragmentation or reaction mode of operation whereinsubstantially fewer ions are fragmented or reacted or whereinsubstantially no ions are fragmented or reacted upon entering the firstion guide or the first collision, fragmentation or reaction device.

In the relatively high fragmentation or reaction mode of operation ionsentering the first ion guide or the first collision, fragmentation orreaction device are preferably accelerated through a potentialdifference selected from the group consisting of: (i) ≧10 V; (ii) ≧20 V;(iii) ≧30 V; (iv) ≧40 V; (v) ≧50 V; (vi) >60 V; (vii) ≧70 V; (viii) ≧80V; (ix) ≧90 V; (x) ≧100 V; (xi) ≧110 V; (xii) ≧120 V; (xiii) ≧130 V;(xiv) ≧140 V; (xv) ≧150 V; (xvi) ≧160 V; (xvii) ≧170 V; (xviii) >180 V;(xix) ≧190 V; and (xx) ≧200 V.

In the relatively low fragmentation or reaction mode of operation ionsentering the first ion guide or the first collision, fragmentation orreaction device are preferably accelerated through a potentialdifference selected from the group consisting of: (i) ≦20 V; (ii) ≦15 V;(iii) ≦10 V; (iv) ≦5V; and (v) ≦1V.

The control system is preferably arranged and adapted to switch thefirst ion guide or the first collision, fragmentation or reaction devicebetween the relatively high fragmentation or reaction mode of operationand the relatively low fragmentation or reaction mode of operation atleast once every 1 ms, 5 ms, 10 ms, 15 ms, 20 ms, 25 ms, 30 ms, 35 ms,40 ms, 45 ms, 50 ms, 55 ms, 60 ms, 65 ms, 70 ms, 75 ms, 80 ms, 85 ms, 90ms, 95 ms, 100 ms, 200 ms, 300 ms, 400 ms, 500 ms, 600 ms, 700 ms, 800ms, 900 ms, 1 s, 2 s, 3 s, 4 s, 5 s, 6 s, 7 s, 8 s, 9 s or 10 s.

The first ion guide or the first collision, fragmentation or reactiondevice is preferably arranged and adapted to receive a beam of ions andto convert or partition the beam of ions such that at least 1, 2, 3, 4,5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19 or 20 separategroups or packets of ions are confined and/or isolated in the first ionguide or the first collision, fragmentation or reaction device at anyparticular time. Each group or packet of ions is preferably separatelyconfined and/or isolated in a separate axial potential well formed inthe first ion guide or the first collision, fragmentation or reactiondevice.

The mass spectrometer preferably further comprises a second ion guide ora second collision, fragmentation or reaction device, wherein the secondion guide or the second collision, fragmentation or reaction device isarranged downstream of the ion mobility spectrometer or separator.

The second ion guide or the second collision, fragmentation or reactiondevice is preferably arranged and adapted to fragment ions by CollisionInduced Dissociation (“CID”).

Alternatively, the second ion guide or the second collision,fragmentation or reaction device may be selected from the groupconsisting of: (i) a Surface Induced Dissociation (“SID”) fragmentationdevice; (ii) an Electron Transfer Dissociation fragmentation device;(iii) an Electron Capture Dissociation fragmentation device; (iv) anElectron Collision or Impact Dissociation fragmentation device; (v) aPhoto Induced Dissociation (“PID”) fragmentation device; (vi) a LaserInduced Dissociation fragmentation device; (vii) an infrared radiationinduced dissociation device; (viii) an ultraviolet radiation induceddissociation device; (ix) a nozzle-skimmer interface fragmentationdevice; (x) an in-source fragmentation device; (xi) an ion-sourceCollision Induced Dissociation fragmentation device; (xii) a thermal ortemperature source fragmentation device; (xiii) an electric fieldinduced fragmentation device; (xiv) a magnetic field inducedfragmentation device; (xv) an enzyme digestion or enzyme degradationfragmentation device; (xvi) an ion-ion reaction fragmentation device;(xvii) an ion-molecule reaction fragmentation device; (xviii) anion-atom reaction fragmentation device; (xix) an ion-metastable ionreaction fragmentation device; (xx) an ion-metastable molecule reactionfragmentation device; (xxi) an ion-metastable atom reactionfragmentation device; (xxii) an ion-ion reaction device for reactingions to form adduct or product ions; (xxiii) an ion-molecule reactiondevice for reacting ions to form adduct or product ions; (xxiv) anion-atom reaction device for reacting ions to form adduct or productions; (xxv) an ion-metastable ion reaction device for reacting ions toform adduct or product ions; (xxvi) an ion-metastable molecule reactiondevice for reacting ions to form adduct or product ions; and (xxvii) anion-metastable atom reaction device for reacting ions to form adduct orproduct ions.

The second ion guide or the second collision, fragmentation or reactiondevice preferably comprises:

(i) a multipole rod set or a segmented multipole rod set;

(ii) an ion tunnel or ion funnel; or

(iii) a stack or array of planar, plate or mesh electrodes.

The multipole rod set preferably comprises a quadrupole rod set, ahexapole rod set, an octapole rod set or a rod set comprising more thaneight rods.

The ion tunnel or ion funnel preferably comprises a plurality ofelectrodes or at least 2, 5, 10, 20, 30, 40, 50, 60, 70, 80, 90 or 100electrodes having apertures through which ions are transmitted in use,wherein at least 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%,60%, 65%, 70%, 75%, 80%, 85%, 90%, 95% or 100% of the electrodes haveapertures which are of substantially the same size or area or which haveapertures which become progressively larger and/or smaller in size or inarea. Preferably, at least 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%,50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95% or 100% of theelectrodes have internal diameters or dimensions selected from the groupconsisting of (i) ≦1.0 mm; (ii) ≦2.0 mm; (iii) ≦3.0 mm; (iv) ≦4.0 mm;(v) ≦5.0 mm; (vi) ≦6.0 mm; (vii) ≦7.0 mm; (viii) ≦8.0 mm; (ix) ≦9.0 mm;(x) ≦10.0 mm; and (xi) >10.0 mm.

The stack or array of planar, plate or mesh electrodes preferablycomprises a plurality or at least 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12,13, 14, 15, 16, 17, 18, 19 or 20 planar, plate or mesh electrodesarranged generally in the plane in which ions travel in use, wherein atleast 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%,70%, 75%, 80%, 85%, 90%, 95% or 100% of the planar, plate or meshelectrodes are arranged generally in the plane in which ions travel inuse.

The mass spectrometer preferably further comprises AC or RF voltagemeans for supplying the plurality of planar, plate or mesh electrodeswith an AC or RF voltage and wherein adjacent planar, plate or meshelectrodes are supplied with opposite phases of the AC or RF voltage.

The second ion guide or the second collision, fragmentation or reactiondevice preferably comprises a plurality of axial segments or at least 5,10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95or 100 axial segments.

According to an embodiment the mass spectrometer preferably furthercomprises transient DC voltage means arranged and adapted to apply oneor more transient DC voltages or potentials or one or more transient DCvoltage or potential waveforms to electrodes forming the second ionguide or the second collision, fragmentation or reaction device in orderto urge at least some ions along at least 5%, 10%, 15%, 20%, 25%, 30%,35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95% or 100%of the axial length of the second ion guide or the second collision,fragmentation or reaction device.

According to another embodiment the mass spectrometer further comprisesAC or RF voltage means arranged and adapted to apply two or morephase-shifted AC or RF voltages to electrodes forming the second ionguide or the second collision, fragmentation or reaction device in orderto urge at least some ions along at least 5%, 10%, 15%, 20%, 25%, 30%,35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95% or 100%of the axial length of the second ion guide or the second collision,fragmentation or reaction device.

The second ion guide or the second collision, fragmentation or reactiondevice preferably has an axial length selected from the group consistingof: (i) <20 mm; (ii) 20-40 mm; (iii) 40-60 mm; (iv) 60-80 mm; (v) 80-100mm; (vi) 100-120 mm; (vii) 120-140 mm; (viii) 140-160 mm; (ix) 160-180mm; (x) 180-200 mm; (xi) 200-220 mm; (xii) 220-240 mm; (xiii) 240-260mm; (xiv) 260-280 mm; (xv) 280-300 mm; and (xvi) >300 mm.

The second ion guide or the second collision, fragmentation or reactiondevice preferably further comprises AC or RF voltage means arranged andadapted to apply an AC or RF voltage to at least 5%, 10%, 15%, 20%, 25%,30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95% or100% of the plurality of electrodes of the second ion guide or thesecond collision, fragmentation or reaction device in order to confineions radially within the second ion guide or the second collision,fragmentation or reaction device.

The AC or RF voltage means is preferably arranged and adapted to supplyan AC or RF voltage to the plurality of electrodes of the second ionguide or the second collision, fragmentation or reaction device havingan amplitude selected from the group consisting of: (i) <50 V peak topeak; (ii) 50-100 V peak to peak; (iii) 100-150 V peak to peak; (iv)150-200 V peak to peak; (v) 200-250 V peak to peak; (vi) 250-300 V peakto peak; (vii) 300-350 V peak to peak; (viii) 350-400 V peak to peak;(ix) 400-450 V peak to peak; (x) 450-500 V peak to peak; and (xi) >500 Vpeak to peak.

The AC or RF voltage means is preferably arranged and adapted to supplyan AC or RF voltage to the plurality of electrodes of the second ionguide or the second collision, fragmentation or reaction device having afrequency selected from the group consisting of: (i) <100 kHz; (ii)100-200 kHz; (iii) 200-300 kHz; (iv) 300-400 kHz; (v) 400-500 kHz; (vi)0.5-1.0 MHz; (vii) 1.0-1.5 MHz; (viii) 1.5-2.0 MHz; (ix) 2.0-2.5 MHz;(x) 2.5-3.0 MHz; (xi) 3.0-3.5 MHz; (xii) 3.5-4.0 MHz; (xiii) 4.0-4.5MHz; (xiv) 4.5-5.0 MHz; (xv) 5.0-5.5 MHz; (xvi) 5.5-6.0 MHz; (xvii)6.0-6.5 MHz; (xviii) 6.5-7.0 MHz; (xix) 7.0-7.5 MHz; (xx) 7.5-8.0 MHz;(xxi) 8.0-8.5 MHz; (xxii) 8.5-9.0 MHz; (xxiii) 9.0-9.5 MHz; (xxiv)9.5-10.0 MHz; and (xxv) >10.0 MHz.

According to an embodiment singly charged ions having a mass to chargeratio in the range of 1-100, 100-200, 200-300, 300-400, 400-500,500-600, 600-700, 700-800, 800-900 or 900-1000 preferably have a driftor transit time through the second ion guide or the second collision,fragmentation or reaction device in the range: (i) 0-10 μs; (ii) 10-20μs; (iii) 20-30 μs; (iv) 30-40 μs; (v) 40-50 μs; (vi) 50-60 μs; (vii)60-70 μs; (viii) 70-80 μs; (ix) 80-90 μs; (x) 90-100 μs; (xi) 100-110μs; (xii) 110-120 μs; (xiii) 120-130 μs; (xiv) 130-140 μs; (xv) 140-150μs; (xvi) 150-160 (xvii) 160-170 μs; (xviii) 170-180 μs; (xix) 180-190μs; (xx) 190-200 μs; (xxi) 200-210 μs; (xxii) 210-220 μs; (xxiii)220-230 μs; (xxiv) 230-240 μs; (xxv) 240-250 (xxvi) 250-260 μs; (xxvii)260-270 μs; (xxviii) 270-280 μs; (xxix) 280-290 μs; (xxx) 290-300 μs;and (xxxi) >300 μs.

The mass spectrometer preferably further comprises means arranged andadapted to maintain at least a portion of the second ion guide or thesecond collision, fragmentation or reaction device at a pressureselected from the group consisting of: (i) >0.0001 mbar; (ii) >0.001mbar; (iii) >0.01 mbar; (iv) >0.1 mbar; (v) >1 mbar; (vi) >10 mbar;(vii) 0.0001-0.1 mbar; and (viii) 0.001-0.01 mbar.

The mass spectrometer preferably further comprises acceleration meansarranged and adapted to accelerate ions emerging from the ion mobilityspectrometer or separator into the second ion guide or the secondcollision, fragmentation or reaction device and wherein in a mode ofoperation at least 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%,60%, 65%, 70%, 75%, 80%, 85%, 90%, 95% or 100% of the ions are caused tofragment or react upon entering the second ion guide or the secondcollision, fragmentation or reaction device.

The acceleration means is preferably arranged and adapted toprogressively vary or increase the kinetic energy of ions emerging fromthe ion mobility spectrometer or separator as they are transmitted tothe second ion guide or the second collision, fragmentation or reactiondevice.

The acceleration means preferably comprises a region across which apotential difference is maintained and wherein the potential differenceis progressively varied or increased with time.

The mass spectrometer preferably further comprises a control systemarranged and adapted to switch or repeatedly switch the potentialdifference through which ions pass prior to entering the second ionguide or the second collision, fragmentation or reaction device betweena relatively high fragmentation or reaction mode of operation whereinions are substantially fragmented or reacted upon entering the secondion guide or the second collision, fragmentation or reaction device anda relatively low fragmentation or reaction mode of operation whereinsubstantially fewer ions are fragmented or reacted or whereinsubstantially no ions are fragmented or reacted upon entering the secondion guide or the second collision, fragmentation or reaction device.

In the relatively high fragmentation or reaction mode of operation ionsentering the second ion guide or the second collision, fragmentation orreaction device are preferably accelerated through a potentialdifference selected from the group consisting of: (i) ≧10 V; (ii) ≧20 V;(iii) ≧30 V; (iv) ≧40 V; (v) ≧50 V; (vi) ≧60 V; (vii) ≧70 V; (viii) ≧80V; (ix) ≧90 V; (x) ≧100 V; (xi) ≧110 V; (xii) ≧120 V; (xiii) 130 V;(xiv) ≧140 V; (xv) ≧150 V; (xvi) ≧160 V; (xvii) ≧170 V; (xviii) ≧180 V;(xix) ≧190 V; and (xx) ≧200 V.

In the relatively low fragmentation or reaction mode of operation ionsentering the second ion guide or the second collision, fragmentation orreaction device are preferably accelerated through a potentialdifference selected from the group consisting of: (i) ≦20 V; (ii) ≦15 V;(iii) ≦10 V; (iv) ≦5V; and (v) ≦1V.

The control system is preferably arranged and adapted to switch thesecond ion guide or the second collision, fragmentation or reactiondevice between the relatively high fragmentation or reaction mode ofoperation and the relatively low fragmentation or reaction mode ofoperation at least once every 1 ms, 5 ms, 10 ms, 15 ms, 20 ms, 25 ms, 30ms, 35 ms, 40 ms, 45 ms, 50 ms, 55 ms, 60 ms, 65 ms, 70 ms, 75 ms, 80ms, 85 ms, 90 ms, 95 ms, 100 ms, 200 ms, 300 ms, 400 ms, 500 ms, 600 ms,700 ms, 800 ms, 900 ms, 1 s, 2 s, 3 s, 4 s, 5 s, 6 s, 7 s, 8 s, 9 s or10 s.

According to an embodiment the second ion guide or the second collision,fragmentation or reaction device is preferably arranged and adapted toreceive a beam of ions from the ion mobility spectrometer or separatorand to convert or partition the beam of ions such that at least 1, 2, 3,4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19 or 20 separategroups or packets of ions are confined and/or isolated in the second ionguide or the second collision, fragmentation or reaction device at anyparticular time. Each group or packet of ions is preferably separatelyconfined and/or isolated in a separate axial potential well formed inthe second ion guide or the second collision, fragmentation or reactiondevice.

The average ion mobility of ions in each of the groups or packets ofions confined and/or isolated in the second ion guide or the secondcollision, fragmentation or reaction device preferably progressivelydecreases with time and/or progressively decreases from the exit regionof the second ion guide or the second collision, fragmentation orreaction device towards the entrance region of the second ion guide orthe second collision, fragmentation or reaction device.

The second ion guide or the second collision, fragmentation or reactiondevice is preferably arranged and adapted to retain and/or confineand/or partition ions emerging from the ion mobility spectrometer orseparator and to translate ions in one or more groups or packets of ionsalong at least 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%,60%, 65%, 70%, 75%, 80%, 85%, 90%, 95% or 100% of the axial length ofthe second ion guide or the second collision, fragmentation or reactiondevice whilst either: (i) substantially maintaining the order and/orfidelity in which ions emerge from the ion mobility spectrometer orseparator; and/or (ii) substantially maintaining the composition of ionsas one or more groups or packets of ions are translated along the secondion guide or the second collision, fragmentation or reaction device.

The ion mobility spectrometer or separator preferably comprises a gasphase electrophoresis device.

According to an embodiment the ion mobility spectrometer or separatorcomprises:

(i) a drift tube;

(ii) a multipole rod set or a segmented multipole rod set;

(iii) an ion tunnel or ion funnel; or

(iv) a stack or array of planar, plate or mesh electrodes.

The drift tube preferably comprises one or more electrodes and means formaintaining an axial DC voltage gradient or a substantially constant orlinear axial DC voltage gradient along at least 5%, 10%, 15%, 20%, 25%,30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95% or100% of the axial length of the drift tube.

The multipole rod set preferably comprises a quadrupole rod set, ahexapole rod set, an octapole rod set or a rod set comprising more thaneight rods.

The ion tunnel or ion funnel preferably comprises a plurality ofelectrodes or at least 2, 5, 10, 20, 30, 40, 50, 60, 70, 80, 90 or 100electrodes having apertures through which ions are transmitted in use,wherein at least 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%,60%, 65%, 70%, 75%, 80%, 85%, 90%, 95% or 100% of the electrodes haveapertures which are of substantially the same size or area or which haveapertures which become progressively larger and/or smaller in size or inarea. Preferably, at least 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%,50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95% or 100% of theelectrodes have internal diameters or dimensions selected from the groupconsisting of (i) ≦1.0 mm; (ii) ≦2.0 mm; (iii) ≦3.0 mm; (iv) ≦4.0 mm;(v) ≦5.0 mm; (vi) ≦6.0 mm; (vii) ≦7.0 mm; (viii) ≦8.0 mm; (ix) ≦9.0 mm;(x) ≦10.0 mm; and (xi) >10.0 mm.

The stack or array of planar, plate or mesh electrodes preferablycomprises a plurality or at least 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12,13, 14, 15, 16, 17, 18, 19 or 20 planar, plate or mesh electrodeswherein at least 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%,60%, 65%, 70%, 75%, 80%, 85%, 90%, 95% or 100% of the planar, plate ormesh electrodes are arranged generally in the plane in which ions travelin use. Preferably, at least some or at least 5%, 10%, 15%, 20%, 25%,30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95% or100% of the planar, plate or mesh electrodes are supplied with an AC orRF voltage and wherein adjacent planar, plate or mesh electrodes aresupplied with opposite phases of the AC or RF voltage.

The ion mobility spectrometer or separator preferably comprises aplurality of axial segments or at least 5, 10, 15, 20, 25, 30, 35, 40,45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95 or 100 axial segments.

According to an embodiment the mass spectrometer preferably comprises DCvoltage means for maintaining a substantially constant DC voltagegradient along at least a portion or at least 5%, 10%, 15%, 20%, 25%,30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95% or100% of the axial length of the ion mobility spectrometer or separatorin order to urge at least some ions along at least a portion or at least5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%,75%, 80%, 85%, 90%, 95% or 100% of the axial length of the ion mobilityspectrometer or separator.

According to an embodiment the mass spectrometer further comprisestransient DC voltage means arranged and adapted to apply one or moretransient DC voltages or potentials or one or more transient DC voltageor potential waveforms to electrodes forming the ion mobilityspectrometer or separator in order to urge at least some ions along atleast 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%,70%, 75%, 80%, 85%, 90%, 95% or 100% of the axial length of the ionmobility spectrometer or separator.

According to an embodiment the mass spectrometer comprises AC or RFvoltage means arranged and adapted to apply two or more phase-shifted ACor RF voltages to electrodes forming the ion mobility spectrometer orseparator in order to urge at least some ions along at least 5%, 10%,15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%,85%, 90%, 95% or 100% of the axial length of the ion mobilityspectrometer or separator.

The ion mobility spectrometer or separator preferably has an axiallength selected from the group consisting of: (i) ≦20 mm; (ii) 20-40 mm;(iii) 40-60 mm; (iv) 60-80 mm; (v) 80-100 mm; (vi) 100-120 mm; (vii)120-140 mm; (viii) 140-160 mm; (ix) 160-180 mm; (x) 180-200 mm; (xi)200-220 mm; (xii) 220-240 mm; (xiii) 240-260 mm; (xiv) 260-280 mm; (xv)280-300 mm; and (xvi) >300 mm

The ion mobility spectrometer or separator preferably further comprisesAC or RF voltage means arranged and adapted to apply an AC or RF voltageto at least 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%,65%, 70%, 75%, 80%, 85%, 90%, 95% or 100% of the plurality of electrodesof the ion mobility spectrometer or separator in order to confine ionsradially within the ion mobility spectrometer or separator.

The AC or RF voltage means is preferably arranged and adapted to supplyan AC or RF voltage to the plurality of electrodes of the ion mobilityspectrometer or separator having an amplitude selected from the groupconsisting of: (i) <50 V peak to peak; (ii) 50-100 V peak to peak; (iii)100-150 V peak to peak; (iv) 150-200 V peak to peak; (v) 200-250 V peakto peak; (vi) 250-300 V peak to peak; (vii) 300-350 V peak to peak;(viii) 350-400 V peak to peak; (ix) 400-450 V peak to peak; (x) 450-500V peak to peak; and (xi) >500 V peak to peak.

The AC or RF voltage means is preferably arranged and adapted to supplyan AC or RF voltage to the plurality of electrodes of the ion mobilityspectrometer or separator having a frequency selected from the groupconsisting of: (i) <100 kHz; (ii) 100-200 kHz; (iii) 200-300 kHz; (iv)300-400 kHz; (v) 400-500 kHz; (vi) 0.5-1.0 MHz; (vii) 1.0-1.5 MHz;(viii) 1.5-2.0 MHz; (ix) 2.0-2.5 MHz; (x) 2.5-3.0 MHz; (xi) 3.0-3.5 MHz;(xii) 3.5-4.0 MHz; (xiii) 4.0-4.5 MHz; (xiv) 4.5-5.0 MHz; (xv) 5.0-5.5MHz; (xvi) 5.5-6.0 MHz; (xvii) 6.0-6.5 MHz; (xviii) 6.5-7.0 MHz; (xix)7.0-7.5 MHz; (xx) 7.5-8.0 MHz; (xxi) 8.0-8.5 MHz; (xxii) 8.5-9.0 MHz;(xxiii) 9.0-9.5 MHz; (xxiv) 9.5-10.0 MHz; and (xxv) >10.0 MHz.

According to an embodiment singly charged ions having a mass to chargeratio in the range of 1-100, 100-200, 200-300, 300-400, 400-500,500-600, 600-700, 700-800, 800-900 or 900-1000 have a drift or transittime through the ion mobility spectrometer or separator in the range:(i) 0-1 ms; (ii) 1-2 ms; (iii) 2-3 ms; (iv) 3-4 ms; (v) 4-5 ms; (vi) 5-6ms; (vii) 6-7 ms; (viii) 7-8 ms; (ix) 8-9 ms; (x) 9-10 ms; (xi) 10-11ms; (xii) 11-12 ms; (xiii) 12-13 ms; (xiv) 13-14 ms; (xv) 14-15 ms;(xvi) 15-16 ms; (xvii) 16-17 ms; (xviii) 17-18 ms; (xix) 18-19 ms; (xx)19-20 ms; (xxi) 20-21 ms; (xxii) 21-22 ms; (xxiii) 22-23 ms; (xxiv)23-24 ms; (xxv) 24-25 ms; (xxvi) 25-26 ms; (xxvii) 26-27 ms; (xxviii)27-28 ms; (xxix) 28-29 ms; (xxx) 29-30 ms; (xxxi) 30-35 ms; (xxxii)35-40 ms; (xxxiii) 40-45 ms; (xxxiv) 45-50 ms; (xxxv) 50-55 ms; (xxxvi)55-60 ms; (xxxvii) 60-65 ms; (xxxviii) 65-70 ms; (xxxix) 70-75 ms; (xl)75-80 ms; (xli) 80-85 ms; (xlii) 85-90 ms; (xliii) 90-95 ms; (xliv)95-100 ms; and (xlv) >100 ms.

According to an embodiment the mass spectrometer further comprises meansarranged and adapted to maintain at least a portion of the ion mobilityspectrometer or separator at a pressure selected from the groupconsisting of: (i) >0.001 mbar; (ii) >0.01 mbar; (iii) >0.1 mbar;(iv) >1 mbar; (v) >10 mbar; (vi) >100 mbar; (vii) 0.001-100 mbar; (viii)0.01-10 mbar; and (ix) 0.1-1 mbar.

The mass spectrometer further comprises means for introducing a firstgas into the ion mobility spectrometer or separator, the first gas beingselected from or at least partially comprising a gas selected from thegroup consisting of: (i) nitrogen; (ii) argon; (iii) helium; (iv)methane; (v) neon; (vi) xenon; and (vii) air.

The mass spectrometer preferably further comprises a housing for the ionmobility spectrometer or separator, the housing forming a substantiallygas tight enclosure apart from an ion entrance aperture, an ion exitaperture and a port for introducing a gas into the housing.

The mass spectrometer preferably further comprises means for pulsingions into the ion mobility spectrometer or separator once every 0-5 ms,5-10 ms, 10-15 ms, 15-20 ms, 20-25 ms, 25-30 ms, 30-35 ms, 35-40 ms,40-45 ms, 45-50 ms, 50-55 ms, 55-60 ms, 60-65 ms, 65-70 ms, 70-75 ms,75-80 ms, 80-85 ms, 85-90 ms, 90-95 ms, 95-100 ms or >100 ms.

The mass spectrometer preferably further comprises an ion source. Theion source is preferably selected from the group consisting of: (i) anElectrospray ionisation (“ESI”) ion source; (ii) an Atmospheric PressurePhoto Ionisation (“APPI”) ion source; (iii) an Atmospheric PressureChemical Ionisation (“APCI”) ion source; (iv) a Matrix Assisted LaserDesorption Ionisation (“MALDI”) ion source; (v) a Laser DesorptionIonisation (“LDI”) ion source; (vi) an Atmospheric Pressure Ionisation(“API”) ion source; (vii) a Desorption Ionisation On Silicon (“DIOS”)ion source; (viii) an Electron Impact (“EI”) ion source; (ix) a ChemicalIonisation (“CI”) ion source; (x) a Field Ionisation (“FI”) ion source;(xi) a Field Desorption (“FD”) ion source; (xii) an Inductively CoupledPlasma (“ICP”) ion source; (xiii) a Fast Atom Bombardment (“FAB”) ionsource; (xiv) a Liquid Secondary Ion Mass Spectrometry (“LSIMS”) ionsource; (xv) a Desorption Electrospray Ionisation (“DESI”) ion source;(xvi) a Nickel-63 radioactive ion source; (xvii) an Atmospheric PressureMatrix Assisted Laser Desorption Ionisation ion source; and (xviii) aThermospray ion source.

The ion source may comprise a pulsed or continuous ion source.

The mass spectrometer may further comprise a mass analyser. The massanalyser may be selected from the group consisting of (i) a quadrupolemass analyser; (ii) a 2D or linear quadrupole mass analyser; (iii) aPaul or 3D quadrupole mass analyser; (iv) a Penning trap mass analyser;(v) an ion trap mass analyser; (vi) a magnetic sector mass analyser;(vii) Ion Cyclotron Resonance (“ICR”) mass analyser; (viii) a FourierTransform Ion Cyclotron Resonance (“FTICR”) mass analyser; (ix) anelectrostatic or orbitrap mass analyser; (x) a Fourier Transformelectrostatic or orbitrap mass analyser; (xi) a Fourier Transform massanalyser; (xii) a Time of Flight mass analyser; (xiii) an orthogonalacceleration Time of Flight mass analyser; and (xiv) an axialacceleration Time of Flight mass analyser.

The mass spectrometer preferably further comprises an ion detector.

According to another aspect of the present invention there is provided amethod of mass spectrometry comprising:

fragmenting or reacting ions in a first ion guide or a first collision,fragmentation or reaction device to produce product, daughter, adduct orfragment ions; and

temporally separating product, daughter, adduct or fragment ionsaccording to their ion mobility which emerge from or which have beentransmitted from the first ion guide or the first collision,fragmentation or reaction device in an ion mobility spectrometer orseparator.

According to another aspect of the present invention there is provided amethod of mass spectrometry comprising:

mass filtering of mass analysing ions in a first mass filter or massanalyser;

temporally separating ions in an ion mobility spectrometer or separator,the ion mobility spectrometer or separator being arranged downstream ofthe first mass filter or mass analyser; and

mass filtering or mass analysing ions in a second mass filter or massanalyser arranged downstream of the ion mobility spectrometer orseparator.

Ions in the ion mobility spectrometer or separator are preferablysubjected to an electric field in the presence of a buffer gas.Different species preferably acquire different velocities and arepreferably separated according to their ion mobility or anotherphysico-chemical property. The mobility of an ion in such a spectrometerdepends on its size, shape and charge.

In a preferred embodiment ions having one or more specific mass tocharge ratios are first transmitted through a mass filter. The ions arethen fragmented or reacted in a collision, fragmentation or reactiondevice. The resulting fragment, daughter, product or adduct ions arethen preferably temporally separated in an ion mobility spectrometer orseparator and detected. The mass filter preferably comprises aquadrupole mass filter although other types of mass filter are alsocontemplated.

According to a preferred embodiment a method of mass spectrometry isprovided comprising fragmenting or reacting ions, providing a pulse offragment, daughter, product or adduct ions and temporally separating atleast some of the ions according to their ion mobility in an ionmobility spectrometer or separator before providing another pulse ofions, and detecting some of the fragment, daughter, product or adductions.

The use of an ion mobility spectrometer or separator rather than a massfilter to analyse fragment or daughter ions has the advantage thatseveral or all of the different fragment or daughter ions may bedetected. This provides a means of detecting more ions than would bedetected using a quadrupole rod set mass filter or mass analyser totransmit only ions having a narrow range of mass to charge ratios. Italso provides a means of measuring the relative abundance of two or morespecific fragment, daughter, product or adduct ions which in turnprovides a means of confirming an analysis. Although a quadrupole rodset mass filter may be programmed to switch to transmit differentfragment or daughter ions for the purpose of confirmation of theanalysis, there is an inevitable corresponding reduction in the dutycycle for the measurement of each specific fragment ion. This leads to aloss in sensitivity for each specific fragment or daughter ion. Incontrast the preferred embodiment comprising an ion mobilityspectrometer or separator separates the different fragment, daughter,product or adduct ions in time such that each species of ion can berecorded without any loss in duty cycle or sensitivity.

According to an embodiment of the present invention ions having one ormore specific mass to charge ratios are transmitted through a first massfilter before being fragmented or reacted in a collision, fragmentationor reaction device. The resulting fragment, daughter, adduct or productions are then preferably temporally separated in an ion mobilityspectrometer or separator. Fragment, daughter, adduct or product ionshaving one or more specific mass to charge ratios are then preferablytransmitted through a second mass filter and the ions are detected by anion detector. The first and second mass filters preferably comprisequadrupole mass filters, although other types of mass filter are alsocontemplated.

According to another embodiment ions having one or more specific mass tocharge ratios are transmitted through a first mass filter before beingfragmented or reacted in a first collision, fragmentation or reactiondevice. The resulting fragment, daughter, adduct or product ions arethen preferably temporally separated in an ion mobility spectrometer orseparator. The fragment, daughter, adduct or product ions are thenpreferably further fragmented in a second collision, fragmentation orreaction device and second generation fragment, daughter, product oradduct ions having one or more specific mass to charge ratios arepreferably transmitted through a second mass filter and are preferablydetected by an ion detector. The first and second mass filterspreferably comprise quadrupole mass filters, although other types ofmass filter are also contemplated.

As in a triple quadrupole mass spectrometer, the specificity of theanalysis may be improved by removing any parent or precursor ions whichmay be present prior to fragmentation or reaction in the collision,fragmentation or reaction device. Ions may be arranged to pass through amass filter positioned upstream of the collision, fragmentation orreaction device. The mass filter preferably comprises a quadrupole rodset mass filter, although other types of mass filter are alsocontemplated. The mass filter may be set so as to transmit all ions orit may be set so as to transmit just selected parent or precursor ionsof interest.

Although the ion mobility spectrometer or separator according to thepreferred embodiment is preferably arranged so as to transmitsubstantially all ions, it may not have as high a specificity as aquadrupole rod set mass filter. The effective resolution of an ionmobility spectrometer or separator may be typically around 20 whereasthe resolution of a quadrupole rod set mass filter may be unit mass i.e.a quadrupole rod set mass filter may have a resolution of 100 at mass tocharge ratio 100, or a resolution of 200 at mass to charge ratio 200, ora resolution of 500 at mass to charge ratio 500 and so on.

In view of the lower resolution of the ion mobility spectrometer orseparator, according to a particularly preferred embodiment ions whichare onwardly transmitted from the ion mobility spectrometer or separatorare preferably passed through a mass filter which is preferablypositioned or arranged downstream of the ion mobility spectrometer orseparator. The mass filter is preferably located upstream of the iondetector.

The mass filter arranged downstream of ion mobility spectrometer orseparator preferably comprises a quadrupole rod set mass filter,although other types of mass filter are also contemplated. The massfilter may be set so as to transmit all ions or it may be set so as totransmit just ions of interest. When set to transmit all ions then theion mobility spectrometer or separator may be used exclusively toanalyse fragment, daughter, product or adduct ions. However, the massfilter may be set so as to transmit a number of specific fragment,daughter, product or adduct ions.

In a preferred embodiment the mass filter arranged downstream of the ionmobility spectrometer or separator may be set so as to switch to anumber of pre-selected mass to charge ratios at pre-selected timesduring the course of the ion mobility separation cycle time. Thepre-selected mass to charge ratio transmission windows may be chosen soas to correspond to the mass to charge ratios of a number of specificfragment, daughter, product or adduct ions of interest. The pre-selectedtimes may be set to encompass the predicted exit or elution times ofthese specifically selected fragment, daughter, product or adduct ionsfrom the ion mobility spectrometer or separator. According to thisembodiment a number of fragment, daughter, product or adduct ions may bemeasured with the specificity of the mass filter but without any loss inthe duty cycle and therefore without any loss in sensitivity.

In another embodiment, the mass filter arranged downstream of the ionmobility spectrometer or separator may be scanned in synchronism withthe ion mobility spectrometer or separator cycle time. The scan law orscan function of the mass filter may be arranged so as to match asclosely as possible the relationship between the mass to charge ratio ofan ion and its exit or elution time from the ion mobility spectrometeror separator such that a substantial number of ions (either parent orprecursor ions or fragment, daughter, product or adduct ions) exitingthe ion mobility spectrometer or separator are subsequently transmittedthrough the mass filter.

The maximum scan rate for a typical quadrupole mass filter is typicallyof the order of 10 to 20 Daltons per ms whilst the experiment run timefor a typical ion mobility spectrometer or separator may typically be ofthe order of 5 to 20 ms. It is apparent that for some applications aconventional quadrupole mass filter may not be able to be scanned fastenough in order to keep up with the arrival rate of ions at the exit theion mobility spectrometer or separator. According to an embodiment thequadrupole mass filter arranged downstream of the ion mobilityspectrometer or separator may be arranged to have a faster scan rate by,for example, reducing the length of the rod set. The ion mobilityspectrometer or separator may also be arranged to have a longer drifttime by, for example, increasing the length of the ion mobilityspectrometer or separator.

According to an embodiment of the present invention there is provided amass spectrometer comprising an ion source, a first mass filter, acollision, fragmentation or reaction device and a means for releasing apacket of fragment, daughter, product or adduct ions in a pulse to thecollision, fragmentation or reaction device. The mass spectrometerpreferably further comprises an ion mobility spectrometer or separator,a second mass filter and an ion detector. A second fragmentation,collision or reaction device may be arranged downstream of the ionmobility spectrometer or separator and upstream of the second massfilter.

The second collision, fragmentation or reaction device preferably allowsfragment, daughter, product or adduct ions which emerge from the ionmobility spectrometer or separator to be further fragmented or reactedso as to form second generation fragment, daughter, product or adductions (i.e. grand-daughter ions). The grand-daughter ions may then besubsequently analysed by the second mass filter.

Each fragment, daughter, product or adduct ion as it exits the ionmobility spectrometer or separator may be fragmented or reacted so as toform a plurality of second generation or grand-daughter ions. One ormore specific grand-daughter ions may be arranged so as to betransmitted through the second mass filter and hence subsequently bedetected by the ion detector. The detection of a specific grand-daughterion from a specific daughter, fragment, product or adduct ion (itselfderived from a specific parent or precursor ion) provides even greaterspecificity. Furthermore, several combinations of daughter, fragment,product or adduct ions and grand-daughter ions from a single parent orprecursor ion may be detected without any reduction in the duty cyclefor the measurement of each grand-daughter ion. Therefore, severalcombinations of daughter, fragment, product or adduct ions andgrand-daughter ions from a single parent or precursor ion may bedetected without any loss of sensitivity.

According to an embodiment there is provided a means for receiving andfragmenting or reacting ions, a means for storing fragment, daughter,product or adduct ions, means for releasing a pulse of ions to an ionmobility spectrometer or separator and a means for detecting ions.

Ions may be received by and fragmented or reacted in a collision cell orother collision, fragmentation or reaction device. The collision cell orother collision, fragmentation or reaction device may be maintained at apressure between 10⁻⁴ mbar and 1 mbar, or more preferably between 10⁻³and 10⁻¹ mbar. The collision cell or other collision, fragmentation orreaction device may comprise an AC or RF ion guide wherein ions areconfined close to the central axis even when undergoing collisions withbackground gas molecules. The RF ion guide may comprise a multipole rodset ion guide wherein an AC or RF voltage is applied betweenneighbouring rods, or a ring stack wherein an AC or RF voltage isapplied between neighbouring rings, or one of many other types of RF ionguide. Ions entering the collision cell with an energy at least 10 eV orgreater may undergo multiple collisions with gas molecules and may beinduced to fragment.

The collision, fragmentation or reaction device may also be used tostore ions and release ions in pulses. A plate or electrode at the exitof the collision, fragmentation or reaction device may be set to avoltage such as to form a potential barrier thereby preventing ions fromexiting the collision, fragmentation or reaction device. For positiveions, a potential of about +10 V with respect to the collision,fragmentation or reaction device may be adequate. A similar plate orelectrode at a similar potential at the entrance to the collision,fragmentation or reaction device may also prevent ions from leaving orexiting the collision, fragmentation or reaction device via theentrance. If the potential on the plate or electrode at the exit of thecollision, fragmentation or reaction device is momentarily lowered to 0V or less than 0 V with respect to the collision, fragmentation orreaction device then ions will be preferably released in a pulse. Therelease of a pulse of ions into the ion mobility spectrometer orseparator preferably marks the start of a new ion mobility separationexperiment.

Ions in the preferred ion mobility spectrometer or separator arepreferably subjected to an electric field in the presence of a buffergas. Different species of ion preferably acquire different velocitiesand preferably become separated according to their ion mobility oranother physico-chemical property. The mobility of an ion in such an ionmobility spectrometer or separator preferably depends upon its size,shape and charge. One form of an ion mobility spectrometer or separatorconsists of a drift tube or cell in which an axial electric field ismaintained. The presence of a buffer gas causes ions having a relativelyhigh ion mobility to pass more quickly through the device than ionshaving a relatively low ion mobility. As a result ions are caused toseparate according to their ion mobility. The drift cell may also act asan ion guide in that ions may be radially confined within the drift cellby the application of an inhomogeneous AC or RF field to the electrodescomprising the drift cell.

The ion mobility spectrometer or separator may be arranged so as toradially confine ions by applying an inhomogeneous AC or RF field to theion guide such that ions are propelled forward by a potential hill orbarrier that preferably moves along the axis of the ion guide in thepresence of a buffer gas. Appropriate selection of the amplitude andvelocity of the travelling potential barrier and the type and pressureof gas preferably allows ions to selectively slip according to their ionmobility. This in turn allows ions of different ion mobility to betransported at different velocities and thereby separated.

The cycle time for an ion mobility separation experiment may be between2 and 50 ms, more preferably between 5 and 20 ms, and yet morepreferably about 10 ms. Ions exiting the ion mobility spectrometer orseparator are preferably detected and recorded. The cycle may then berepeated.

An ion source may be provided which preferably comprises a pulsed ionsource such as a Laser Desorption Ionisation ion source, a MatrixAssisted Laser Desorption/Ionisation ion source or aDesorption/Ionisation on Silicon ion sources.

Alternatively, a continuous ion source may be used. The continuous ionsource may comprise an Electrospray Ionisation ion source, anAtmospheric Pressure Chemical Ionisation ion source, an Electron Impaction source, an Atmospheric Pressure Photon Ionisation ion source, aChemical Ionisation ion source, a Fast Atom Bombardment ion source, aLiquid Secondary Ion Mass Spectrometry ion source, a Field Ionisationion source, a Field Desorption ion sources. Other continuous orpseudo-continuous ion sources may also be used.

The mass spectrometer may comprise a mass filter arranged downstream ofthe ion source and upstream of the collision, fragmentation or reactiondevice. The mass filter may be used to transmit ions having a singlespecific mass to charge ratio or ions having a range of mass to chargeratios. The mass filter may comprise a multipole rod set mass filter, aquadrupole mass filter, a Time of Flight mass filter, a Wein filter or amagnetic sector mass filter or mass analyser.

The mass spectrometer may comprise a second mass filter preferablyarranged downstream of the ion mobility spectrometer or separator andpreferably upstream of the ion detector. The second mass filter may bearranged to transmit ions having a single specific mass to charge ratioor ions having a range of mass to charge ratios. The second mass filtermay comprise a multipole rod set mass filter, a quadrupole mass filter,a Time of Flight mass filter, a Wein filter, or a magnetic sector massfilter or mass analyser.

The mass spectrometer may also comprise a second collision,fragmentation or reaction device arranged downstream of the ion mobilityspectrometer or separator and preferably upstream of the second massfilter. In one mode of operation at least some ions entering the secondcollision, fragmentation or reaction device are preferably caused tofragment or reset.

The second collision, fragmentation or reaction cell may be maintainedat a pressure between 10⁻⁴ mbar and 1 mbar, or more preferably between10⁻³ and 10⁻¹ mbar. The second collision, fragmentation or reactiondevice may include an AC or RF ion guide to confine the ions close tothe central axis even when undergoing collisions with background gasmolecules. The AC or RF ion guide may comprise a multipole rod set ionguide wherein an AC or RF voltage is applied between neighbouring rods,or a ring stack with RF voltage applied between neighbouring rings, orone of many other types of AC or RF ion guide. Ions entering the secondcollision, fragmentation or reaction device with an energy at least 10eV or greater may preferably undergo multiple collisions with gasmolecules and may be induced to fragment.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments of the present invention will now be described, byway of example only, and with reference to the accompanying drawings inwhich:

FIG. 1 shows a conventional triple quadrupole mass spectrometer;

FIG. 2 shows a first embodiment of the present invention comprising afirst mass filter, a collision, fragmentation or reaction device, an ionmobility spectrometer or separator, an ion guide and an ion detector;

FIG. 3 shows a second embodiment of the present invention comprising afirst mass filter, a collision, fragmentation or reaction device, an ionmobility spectrometer or separator, an ion guide, a second mass filterand an ion detector;

FIG. 4 shows an Electrospray mass spectrum for the peptideGlu-Fibrinopeptide B;

FIG. 5 shows an ion mobility spectrum of the peptide Glu-FibrinopeptideB and an ion mobility spectrum of the fragments of the peptideGlu-Fibrinopeptide B;

FIG. 6 shows a mass spectrum of the fragment ions resulting fromfragmentation of the doubly charged ion of the peptideGlu-Fibrinopeptide B; and

FIG. 7 shows an ion mobility spectrum of all the fragment ions from thedoubly charged ion of the peptide Glu-Fibrinopeptide B and an ionmobility spectrum showing a number of specific fragment ions from thedoubly charged ion of the peptide Glu-Fibrinopeptide B.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A conventional triple quadrupole mass spectrometer is shown in FIG. 1.Ions 1 from an ion source (not shown) are passed to a quadrupole rod setmass filter 2. The quadrupole rod set mass filter 2 is arranged toselectively transmit parent or precursor ions having a specific mass tocharge ratio. The selected parent or precursor ions are then onwardlytransmitted and accelerated into a collision cell 3 comprising arelatively high pressure quadrupole rod set ion guide supplied with acollision gas.

The selected parent or precursor ions which enter the collision cell 3undergo multiple collisions with collision gas molecules present in thecollision cell 3. The parent or precursor ions are induced to fragmentforming fragment or daughter ions in the process. The resulting fragmentor daughter ions and any unfragmented precursor or parent ions are thenpassed from the collision cell 3 to a quadrupole rod set mass analyser 4which is arranged downstream of the collision cell 3. The quadrupole rodset mass analyser 4 arranged downstream of the collision cell 3 may bescanned. Fragment or daughter ions transmitted by the quadrupole rod setmass analyser 4 are then detected by an ion detector 5 which is arrangeddownstream of the quadrupole rod set mass analyser 4.

The quadrupole rod set mass filter 2 arranged upstream of the collisioncell 3 and the quadrupole mass analyser 4 arranged downstream of thecollision cell 3 may be operated so as to transmit ions having a singleor a specific mass to charge ratio. The quadrupole mass filter 2upstream of the collision cell 3 and the quadrupole rod set massanalyser 4 arranged downstream of the collision cell 3 will have dutycycle of substantially 100% when they are operated so as to transmitions having a single specific mass to charge ratio.

The triple quadrupole mass spectrometer may be used to perform SelectedReaction Monitoring (SRM) experiments wherein specific parent orprecursor ions are transmitted by the quadrupole mass filter 2 and arethen fragmented in the collision cell 3. The quadrupole mass analyser 4arranged downstream of the collision cell 3 may be set to monitor forspecific fragment or daughter ions. Such an arrangement is very specificand exceptionally sensitive.

Triple quadrupole mass spectrometers have found significant use in thefield of drug discovery and development where they may be used in bothSRM and also MRM (Multiple Reaction Monitoring) modes to quantify targetcompounds.

FIG. 2 shows a mass spectrometer according to a first embodiment of thepresent invention. The mass spectrometer preferably comprises aquadrupole rod set mass filter 7, a collision, fragmentation or reactiondevice 8, an ion mobility spectrometer or separator 10, an ion guide 13arranged downstream of the ion mobility spectrometer or separator 10 andan ion detector 15.

A continuous ion source (not shown) such as an Electrospray ion sourcemay be provided. The ion source preferably generates a beam of ions 6which are preferably passed to the quadrupole rod set mass filter 7arranged upstream of the collision, fragmentation or reaction device 8.

Certain specific parent or precursor ions may be arranged so as to beselectively transmitted by the quadrupole rod set mass filter 7 andpassed to the collision, fragmentation or reaction device 8 which ispreferably arranged downstream of the quadrupole rod set mass filter 7.

In one embodiment the collision, fragmentation or reaction device 8 mayalso function as an ion trap. Parent or precursor ions may be arrangedto enter the collision, fragmentation or reaction device 8 and accordingto an embodiment undergo multiple collisions with background gasmolecules present in the collision, fragmentation or reaction device 8.The parent or precursor ions are preferably induced to react or fragmentso as to form fragment, daughter, adduct or product ions. The resultingfragment, daughter, adduct or product ions and any remainingunfragmented parent or precursor ions are preferably trapped in thecollision, fragmentation or reaction device 8.

Ions trapped within the collision, fragmentation or reaction device 8may then preferably be pulsed out of the collision, fragmentation orreaction device 8 by, for example, the application of an extractionvoltage to an ion gate 9 which is preferably located generally at theexit of the collision, fragmentation or reaction device 8. The ionswhich are pulsed or ejected out of the collision, fragmentation orreaction device 8 then preferably pass to an ion mobility spectrometeror separator 10 which is preferably arranged downstream of thecollision, fragmentation or reaction device 8.

The collision, fragmentation or reaction device 8 may according to anembodiment comprise a quadrupole rod set or other multipole rod setpreferably having a length of approximately 75 mm. According to anotherembodiment the collision, fragmentation or reaction device 8 maycomprise an ion tunnel ion guide comprising a plurality of electrodeshaving apertures therein. The apertures of the electrodes are preferablyall the same size. In other embodiments at least 60%, 65%, 70%, 75%,80%, 85%, 90% or 95% of the electrodes of the collision, fragmentationor reaction device 8 have apertures which are substantially the samesize. The collision, fragmentation or reaction device 8 may preferablycomprise approximately 50 electrodes. Adjacent electrodes are preferablyconnected to opposite phases of a two-phase AC or RF voltage supply. TheAC or RF voltage applied to the electrodes preferably causes apseudo-potential well to be generated which preferably acts to radiallyconfine ions within the collision, fragmentation or reaction device 8.

In the preferred embodiment the electrodes comprising the collision,fragmentation or reaction device 8 are preferably maintained at a DCvoltage V1. The ion gate 9 downstream of the collision, fragmentation orreaction device 8 is preferably normally held at a DC voltage V2 whichis preferably higher than V1. The voltage applied to the ion gate 9 maybe periodically dropped or lowered to a voltage V3 which is preferablylower than V1. Ions may therefore be caused to be accelerated out of theion collision, fragmentation or reaction device 8. The ions are thenpreferably admitted or pulsed into the ion mobility spectrometer orseparator 10.

Adjacent electrodes which form the collision, fragmentation or reactiondevice 8 may be connected to opposite phases of an AC or RF voltagesupply. The AC or RF voltage supply preferably has a frequency withinthe range 0.1-3.0 MHz, preferably 0.3-2.0 MHz, further preferably0.5-1.5 MHz.

According to another embodiment, a pulsed ion source such as a MatrixAssisted Laser Desorption Ionisation (“MALDI”) ion source or a LaserDesorption Ionisation ion source may be used instead of a continuous ionsource. If a pulsed ion source is used then ion gate 9 may be omitted.

The ion mobility spectrometer or separator 10 preferably causes ions tobecome temporally separated according to their ion mobility. The ionmobility spectrometer or separator 10 may comprise a number of differentforms.

In one embodiment the ion mobility spectrometer or separator 10 maycomprise a drift tube comprising a number of guard rings distributedwithin the drift tube. The guard rings may be interconnected byequivalent valued resistors and may be connected to a DC voltage source.A linear DC voltage gradient may be generated which is preferablymaintained along at least a portion of the length of the drift tube. Theguard rings may not be connected to an AC or RF voltage source i.e. ionsmay not be radially confined within the ion mobility spectrometer orseparator 10 according to this embodiment.

According to another embodiment the ion mobility spectrometer orseparator 10 may comprise a number of ring, annular or plate electrodes.The electrodes preferably have an aperture therein through which ionsare preferably transmitted. The apertures are preferably all the samesize and are preferably circular. In other embodiments at least 60%,65%, 70%, 75%, 80%, 85%, 90% or 95% of the electrodes have apertureswhich are substantially the same size or area. The ion mobilityspectrometer or separator 10 may comprise a plurality of electrodesarranged in a vacuum chamber.

The ion mobility spectrometer or separator 10 preferably has a length ofbetween 100 mm and 200 mm. The ion mobility spectrometer or separator 10is preferably provided in a vacuum chamber which is preferablymaintained, in use, at a pressure within the range 0.1-10 mbar.According to less preferred embodiments, the vacuum chamber may bemaintained at a pressure greater than 10 mbar up to a pressure at ornear atmospheric pressure. Also, according to less preferredembodiments, the vacuum chamber may alternatively be maintained at apressure below 0.1 mbar.

Alternate electrodes of the ion mobility spectrometer or separator 10are preferably coupled to opposite phases of a two-phase AC or RFvoltage supply. The AC or RF voltage supply preferably has a frequencywithin the range 0.1-3.0 MHz, preferably 0.3-2.0 MHz, further preferably0.5-1.5 MHz.

The electrodes comprising the collision, fragmentation or reactiondevice 8 and the electrodes comprising the ion mobility spectrometer orseparator 10 may preferably be interconnected via resistors to a DCvoltage supply which may comprise a 400 V supply. The resistorsinterconnecting electrodes forming the ion mobility spectrometer orseparator 10 may be substantially equal in value in which case a linearaxial DC voltage gradient may preferably be maintained along the lengthof the ion mobility spectrometer or separator 10. The DC voltagegradient may be linear or non-linear. According to an embodiment the DCvoltage gradient is preferably stepped. The applied AC or RF voltage ispreferably superimposed upon the DC voltage and serves to radiallyconfine ions within the ion mobility spectrometer or separator 10. TheDC voltages V2 or V3 applied to the ion gate 9 preferably float on theDC voltage supply. The AC or RF voltage supply is preferably isolatedfrom the DC voltage supply by a capacitor.

In another embodiment the ion mobility spectrometer or separator 10 maycomprise an ion guide comprising of a plurality of electrodes havingapertures through which ions are transmitted in use. One or moretransient DC voltages or potentials or one or more transient DC voltageor potential waveforms are preferably progressively applied to theelectrodes. The apertures of the electrodes forming the ion mobilityspectrometer or separator 10 are preferably all the same size. In otherembodiments at least 60%, 65%, 70%, 75%, 80%, 85%, 90% or 95% of theelectrodes have apertures which are substantially the same size.Adjacent electrodes are preferably connected to opposite phases of atwo-phase AC or RF supply. One or more transient DC voltages orpotentials or one or more transient DC voltage or potential waveformsare preferably applied to one or more electrodes of the ion mobilityspectrometer or separator 10 in order to form one or more potentialhills or barriers which are preferably translated along the length ofthe ion mobility spectrometer or separator 10. The one or more transientDC voltages or potentials or one or more transient DC voltage orpotential waveforms are preferably progressively applied to a successionof electrodes forming the ion mobility spectrometer or separator suchthat the one or more potential hills or barriers move along the axis ofthe ion mobility spectrometer or separator 10 in the direction in whichthe ions are to be propelled or driven.

The ion mobility spectrometer or separator 10 is preferably provided ina vacuum chamber that is preferably maintained, in use, at a pressurewithin the range 0.1-10 mbar. According to a less preferred embodiment,the vacuum chamber may be maintained at a pressure greater than 10 mbarup to a pressure at or near atmospheric pressure. According to anotherless preferred embodiment the vacuum chamber may be maintained at apressure below 0.1 mbar.

The presence of gas which the ion mobility spectrometer or separator 10preferably imposes a viscous drag on the movement of ions and theamplitude and average velocity of the one or more potential hills orbarriers is preferably set such that ions will, from time to time, slipover a potential hill or barrier. The lower the mobility of the ion themore likely the ion will be to slip or otherwise pass over a potentialhill. This in turn allows ions having different ion mobilities to betransported at different velocities through the ion mobilityspectrometer or separator 10 and therefore to become temporallyseparated.

Typical drift times through the preferred ion mobility spectrometer orseparator 10 are of the order of a several milliseconds. After all theions which have been pulsed into the ion mobility spectrometer orseparator 10 have traversed the length of the ion mobility spectrometeror separator 10, a new pulse of ions is preferably admitted or pulsedinto the ion mobility spectrometer or separator 10 which preferablymarks the start of a new cycle of operation. Many cycles may beperformed in a single experiment.

According to a preferred embodiment a differential pumping aperture 12may preferably be provided downstream of the ion mobility spectrometeror separator 10. An ion guide 13 may also be provided downstream of theion mobility spectrometer or separator 10. A further differentialpumping aperture 14 may be provided downstream of the ion guide 13. Avacuum chamber housing an ion detector 15 may be arranged downstream ofthe further differential pumping aperture 14. The ion guide 13 may forman intermediate vacuum stage between that of the ion mobilityspectrometer or separator 10 and that of the ion detector 15. Accordingto an embodiment, the ion guide 13 may be maintained at substantiallythe same pressure as that of the collision, fragmentation or reactiondevice 8.

The ion guide 13 may comprise a quadrupole rod set or other multipolerod set and preferably has a length of approximately 75 mm.Alternatively, the ion guide 13 may comprise an ion tunnel ion guidecomprising a plurality of electrodes having apertures therein. Theapertures are preferably all the same size. In other embodiments atleast 60%, 65%, 70%, 75%, 80%, 85%, 90% or 95% of the electrodes haveapertures which are substantially the same size. The ion tunnel ionguide 13 may preferably comprise approximately 50 electrodes. Adjacentelectrodes of the ion guide 13 are preferably connected to oppositephases of a two-phase AC or RF voltage supply so that ions are radiallyconfined in use within the ion tunnel ion guide 13.

According to a particularly preferred embodiment the ion guide 13 maycomprise an ion tunnel ion guide wherein one or more transient DCvoltages or potentials or one or more transient DC voltage or potentialwaveforms are applied to the electrodes forming the ion guide 13. Theapertures of the electrodes forming the ion guide 13 are preferably allthe same size. In other embodiments at least 60%, 65%, 70%, 75%, 80%,85%, 90% or 95% of the electrodes have apertures which are substantiallythe same size. Adjacent electrodes are preferably connected to oppositephases of a two-phase AC or RF supply.

The one or more transient DC voltages or one or more transient DCvoltage waveforms applied to the electrodes of the ion guide 13preferably form one or more potential hills or barriers. The one or moretransient DC voltages or potentials or one or more transient DC voltageor potential waveforms are preferably progressively applied to asuccession of electrodes of the ion guide 13 such that the one or morepotential hills or barriers preferably move along the axis of the ionguide 13 towards the exit of the ion guide 13.

The ion guide 13 is preferably provided in a vacuum chamber which ispreferably maintained, in use, at a pressure within the range 10⁻³ mbarto 10⁻¹ mbar. According to a less preferred embodiment, the vacuumchamber may be maintained at a pressure greater than 10⁻³ mbar up to apressure at or near 1 mbar. According to another less preferredembodiment the vacuum chamber may be maintained at a pressure below 10⁻³mbar.

The gas pressure is preferably sufficient to impose collisional dampingof ion motion, but is preferably not sufficient so as to imposeexcessive viscous drag on the movement of ions. The amplitude andaverage velocity of the one or more potential hills or barriers ispreferably set such that ions will not slip over a potential hill orbarrier. The ions are preferably transported ahead of each travellingpotential hill or barrier regardless of their mass, or mass to chargeratio, or mobility.

The advantage of providing an ion guide 13 wherein one or more transientDC voltages or potentials or one or more transient DC voltage orpotential waveforms are preferably applied to the electrodes forming theion guide 13 is that the temporal separation of the ions exiting the ionmobility spectrometer or separator 10 may be maintained as the ions aretransported by the ion guide 13 to the ion detector 15. The ion detector15 is preferably able to record an ion mobility spectrum of fragmentions without any loss in resolution or specificity.

FIG. 3 shows a second embodiment of the present invention which issubstantially similar in many respects to the first embodiment.According to this embodiment a second mass filter 16 is preferablyadditionally provided downstream of the ion guide 13 which is preferablyarranged downstream of the ion mobility spectrometer or separator 10.The second mass filter 16 is preferably arranged upstream of the iondetector 15. As in the first embodiment illustrated in FIG. 2, acontinuous ion source (e.g. an Electrospray ion source) preferablygenerates a beam of ions 6 which are then preferably passed to a firstquadrupole rod set mass filter 7.

The ion sources and other aspects described in relation to the firstmain preferred embodiment may also be used or provided in relation tothe second main preferred embodiment.

The first quadrupole rod set mass filter 7 is arranged to onwardlytransmit certain specific parent or precursor ions which are thenpreferably arranged to enter a collision, fragmentation or reactiondevice 8 which is preferably arranged downstream of the first quadrupolerod set mass filter 7. The collision, fragmentation or reaction device 8is preferably also arranged so as to trap ions. Ions in the collision,fragmentation or reaction device 8 may according to an embodimentundergo multiple collisions with background gas molecules and may beinduced to fragment. Fragment, daughter, adduct or product ions and anyremaining unfragmented parent or precursor ions are preferably trappedin the collision, fragmentation or reaction device 8. The ions are thenpreferably pulsed or ejected out of the collision, fragmentation orreaction device 8 by, for example, the application of an extractionvoltage to an ion gate 9 which is preferably arranged at the exit of thecollision, fragmentation or reaction device 8.

An ion mobility spectrometer or separator 10 is preferably arranged sdownstream of the collision, fragmentation or reaction device 8. The ionmobility spectrometer or separator 10 is preferably arranged to receiveions emitted from the collision, fragmentation, or reaction device 8.

The ion mobility spectrometer or separator 10 may comprise a drift tubehaving a number of guard rings distributed within the drift tube. Inanother embodiment alternate electrodes forming the ion mobilityspectrometer or separator 10 may preferably be coupled to oppositephases of a two-phase AC or RF voltage supply. In another embodiment theion mobility spectrometer or separator 10 may comprise a plurality ofelectrodes having apertures through which ions are transmitted in use.One or more transient DC voltages or potentials or one or more transientDC voltage or potential waveforms may be applied to the electrodescomprising the ion mobility spectrometer or separator 10.

A differential pumping aperture 12 may be provided downstream of the ionmobility spectrometer or separator 10. An ion guide 13 is preferablyarranged downstream of the differential pumping aperture 12. A furtherdifferential pumping aperture 14 may be provided downstream of the ionguide 13. A second quadrupole rod set mass filter 16 is preferablyprovided downstream of the further differential pumping aperture 14.Ions transmitted by the second quadrupole mass filter 16 are preferablydetected by an ion detector 15 which is preferably arranged downstreamof the second quadrupole rod set mass filter 16.

The ion guide 13 arranged downstream of the ion mobility spectrometer orseparator 10 preferably provides an intermediate vacuum stage betweenthat of the ion mobility spectrometer or separator 10 and that of thesecond quadrupole rod set mass filter 16 and the ion detector 15. Forconvenience, the ion guide 13 may be maintained at the same pressure asthat of the collision, fragmentation or reaction device 8 arrangedupstream of the ion mobility spectrometer or separator 10.

The ion guide 13 arranged downstream of the ion mobility spectrometer orseparator 10 may comprise a quadrupole rod set, or other multipole rodset. Alternatively, the ion guide 13 may comprise an ion tunnel ionguide comprising a plurality of electrodes having apertures therein. Oneor more transient DC voltages or potentials or one or more voltage orpotential waveforms may be applied to the electrodes of the ion guide13. The gas pressure in the ion guide 13 may be sufficient so as toimpose collisional damping of ion motion. The gas pressure is preferablynot sufficient so as to impose excessive viscous drag on the movement ofions. Ions are preferably transported ahead of each travelling potentialhill or barrier regardless of their mass, mass to charge ratio or ionmobility.

The advantage of using an ion guide 13 wherein one or more transient DCvoltages or potentials or one or more transient DC voltage or potentialwaveforms are applied to the electrodes of the ion guide 13 is that thetemporal separation of the ions exiting the ion mobility spectrometer orseparator 10 can preferably be maintained as the ions are transported toor towards the second mass filter 16 and onwards to the ion detector 15.

The second mass filter 16 preferably comprises a quadrupole rod set massfilter. However, according to other less preferred embodiments thesecond mass filter 16 may comprise a different form of mass filter. Thesecond mass filter 16 may be arranged so as to transmit all ions i.e.the second mass filter 16 may be operated in a non-resolving or ionguiding mode of operation. Alternatively, the second mass filter 16 maybe arranged to transmit ions having a specific mass to charge ratio orhaving a range of mass to charge ratios.

In one mode of operation the second mass filter 16 may be set so as totransmit a single species of fragment, daughter, adduct or product ionsduring the course of an ion mobility separation cycle i.e. during thecourse of ions emerging from the ion mobility spectrometer or separator10 and prior to a new pulse of ions being admitted into the ion mobilityspectrometer or separator 10. The recording of a fragment, daughter,product or adduct ion with a specific mass to charge ratio and at aspecific ion mobility elution time provides increased specificity of themeasurement.

In another mode of operation the second mass filter 16 may be set so asto transmit a number of different specific fragment, daughter, productor adduct ions at a number of different specific ion mobility elutiontimes. This provides the opportunity to measure more than one fragment,daughter, product or adduct ion without any loss in sensitivity for eachfragment, daughter, product or adduct mass. Since more than onefragment, daughter, product or adduct ion may be measured, the totalsignal measured will be increased compared to the situation when just asingle fragment, daughter, product or adduct mass is measured. Therecording of a number of different fragment, daughter, product or adductions each having a specific mass to charge ratio and a specific ionmobility elution time provides an increased specificity for eachmeasurement. The recording of several fragment, daughter, product oradduct ions, each with high specificity, allows the relative abundanceof each fragment, daughter, product or adduct mass to be comparedthereby providing a means of further validating the measurement.

In another mode of operation the second mass filter 16 may be scanned inorder to transmit several or all of the different ions as they elutefrom the ion mobility spectrometer or separator 10. The scan law or scanfunction of the second mass filter 16 may be set so as to match asclosely as possible the known elution time from the ion mobilityspectrometer or separator 10 of ions having one or more specific chargestates. This provides the opportunity to measure several or all of theparent, precursor or fragment, daughter, product or adduct ions with ahigh sampling duty cycle. This in turn provides a means of recording thecomplete parent or precursor or fragment, daughter, product or adduction mass spectrum using a quadrupole mass filter with increasedsensitivity.

The transit time of ions through a conventional quadrupole rod set massfilter may be too long to allow the quadrupole mass filter to be scannedquickly enough in order to keep up with the arrival of ions from the ionmobility spectrometer or separator 10. For example, the time for ionshaving an energy of 3 eV to pass through a 130 mm long quadrupole rodset mass filter is 5.45 √(m/z) μs where m/z is the mass to charge ratioof the ion. Ions having a mass to charge ratio of 200 would, forexample, have a transit time of 77 μs. For ions having a mass to chargeratio of 400 the transit time would be 110 μs. Hence, the maximum scanrate is approximately of the order of 100 μs per mass unit or 100 ms per1000 mass units. This may be too slow to keep up with an ion mobilityspectrometer or separator experiment if the drift time of ions having amass to charge ratio of 1000 through the ion mobility spectrometer orseparator 10 was approximately 10 ms.

According to a preferred embodiment a quadrupole mass filter 16 having afaster scan rate and/or an ion mobility spectrometer or separator 10having longer drift times may be used. The scan rate of the second massfilter 16 may be increased by reducing the length of the second massfilter 16, for example, to 50 mm and/or by increasing the ion energy,for example, to 5 eV. For this arrangement the scan rate would increaseby a factor of approximately ×3.

The drift times through the ion mobility spectrometer or separator 10can also be increased by at least a factor ×3 by increasing the lengthof the ion mobility spectrometer or separator 10 and reducing the fieldstrength or the amplitude of the travelling wave (i.e. transient DCvoltage or potential) applied to the electrodes of the ion mobilityspectrometer or separator 10.

According to an embodiment the second mass filter 16 may be scanned at arate compatible with the arrival of ions from the ion mobilityspectrometer or separator 10. This enables the sensitivity of thescanning quadrupole mass filter 16 to be increased for both parent orprecursor ion and also fragment, daughter, product or adduct ion massanalysis.

In another mode of operation fragment, daughter, product or adduct ionsmay be arranged so that they are sufficiently energetic when they enterthe ion guide 13 that when they collide with gas molecules present inthe ion guide 13 they are caused to fragment into second generationfragment, daughter, product or adduct ions or grand-daughter ions.Subsequent transmission of a specific grand-daughter or secondgeneration ion through the second mass filter 16 and onwards to the iondetector 15 allows the monitoring of a two stage reaction. In certaininstances this can provide additional specificity to the measurement.

In another mode of operation fragment, daughter, product or adduct ionsmay be induced to fragment or react so to as to form second generationfragment, daughter, product or adduct ions in the ion guide 13 and thesecond mass filter 16 may be set to transmit several different specificions at a number of different specific ion mobility elution times. Thisallows several different second generation fragment, daughter, productor adduct ions to be measured during the course of the ion mobilitycycle time. Each second generation fragment, daughter, product or adduction may be measured without significant loss in sensitivity, therebyincreasing the overall sensitivity. In certain instances theseadditional measurements can provide a means of further validating themeasurement.

In another mode of operation different fragment, daughter, product oradduct ions may be arranged so that they have different kinetic energieswhen they enter the ion guide 13. The different kinetic energies may beselected such that the efficiency of fragmentation or reaction to formselected second generation fragment, daughter, product or adduct ion isoptimised for each fragment ion.

The ion kinetic energy may also be set so that selected fragment,daughter, product or adduct ions enter the ion guide 13 with a lowkinetic energy and are not induced to fragment or react. Hence, in onecycle of an ion mobility separation experiment the kinetic energy offragment, daughter, product or adduct ions may be programmed to severaldifferent values and the second mass filter 16 may be programmed totransmit several different species of ions in synchronism. The differentspecies of ions transmitted by the second mass filter 16 to the iondetector 15 in one cycle of an ion mobility experiment may, for example,comprise all first generation fragment, daughter, product or adduct ionsor all second generation fragment, daughter, product or adduct ions or amixture of first and second generation fragment, daughter, product oradduct ions.

The energy of ions entering the ion guide 13 can preferably becontrolled, for example, by setting the level of a voltage differenceexperienced by ions prior to entering the ion guide 13. Since thevoltage difference can be switched near instantaneously, the ion guide13 can, in effect, be considered to be switchable between a relativelyhigh fragmentation or reaction mode of operation and a relatively lowfragmentation or reaction mode of operation.

The collision, fragmentation or reaction device 8 may serve the functionof an ion trap and may be arranged to store fragment, daughter, productor adduct ions and to release them in pulses to the ion mobilityspectrometer or separator 10. In a preferred embodiment the collision,fragmentation or reaction device 8 may comprise an ion guide wherein oneor more transient DC voltages or potentials or one or more transient DCvoltage or potential waveforms are applied to the electrodes comprisingthe collision, fragmentation or reaction device 8.

The apertures of the electrodes forming the collision, fragmentation orreaction device 8 are preferably all the same size. Adjacent electrodesare preferably connected to the opposite phases of an AC or RF supply.One or more transient DC voltages or potentials or one or more transientDC voltage or potential waveforms are preferably applied to one or moreelectrodes of the collision, fragmentation or reaction device 8 in orderto form one or more potential hills or barriers. The one or moretransient DC voltages or potentials or one or more transient DC voltageor potential waveforms are preferably progressively applied to asuccession of electrodes of the collision, fragmentation or reactiondevice 8 such that the one or more potential hills or barrierspreferably move along the axis of the collision, fragmentation orreaction device 8 in the direction in which the ions are to be propelledor driven.

The collision, fragmentation or reaction device 8 is preferably providedin a vacuum chamber which is preferably maintained, in use, at apressure within the range 10⁻³ mbar to 10⁻¹ mbar. According to lesspreferred embodiments, the vacuum chamber may be maintained at apressure greater than 10⁻¹ mbar up to a pressure at or near 1 mbar.According to other less preferred embodiments, the vacuum chamber mayalternatively be maintained at a pressure below 10⁻³ mbar. The gaspressure is preferably sufficient to impose collisional damping of ionmotion but is preferably not sufficient so as to impose excessiveviscous drag on the movement of ions. The amplitude and average velocityof the one or more potential hills or barriers is preferably set suchthat ions will not slip over a potential hill or barrier. The ions arepreferably transported ahead of each travelling potential hill orbarrier regardless of their mass, mass to charge ratio or ion mobility.

Ions may be transported in the collision, fragmentation or reactiondevice 8 and are preferably released as packets to the ion mobilityspectrometer or separator 10. The wave cycle time of the collision,fragmentation or reaction device 8 is preferably equal to the cycle timeof the ion mobility spectrometer or separator 10. Alternatively, ionsmay be accumulated and held in a trapping region near the exit of thecollision, fragmentation or reaction device 8 and released to the ionmobility spectrometer or separator 10 at the start of each cycle of anion mobility separation experiment. In this mode of operation the wavecycle time of the collision, fragmentation or reaction device 8 may notmatch that of the ion mobility spectrometer or separator 10.

The pressure in the collision, fragmentation or reaction device 8 mayaccording to an embodiment be substantially the same as that in the ionguide 13. In a preferred embodiment the collision, fragmentation orreaction device 8 and the ion guide 13 are preferably located in thesame vacuum chamber. The ion mobility spectrometer or separator 10 maybe contained or otherwise housed within an inner chamber positionedwithin the vacuum chamber housing the collision, fragmentation orreaction device 8 and the ion guide 13. A collision gas, preferablynitrogen or argon, may be leaked or supplied into the inner chamber inorder to maintain the inner chamber at a preferred pressure between 0.1and 10 mbar. The collision gas may leak into the outer chamber throughan entrance and an exit aperture of the inner chamber. The outer chamberis preferably pumped such as to maintain a pressure in the outer chamberwithin the range 0.001 and 0.01 mbar.

FIG. 4 shows a mass spectrum of the peptide Glu-Fibrinopeptide Bproduced by ionising a sample using an Electrospray ion source. It canbe seen that the most abundant ion is the doubly protonated ion M+2H 2+having a mass to charge ratio of 785.8

FIG. 5 shows an ion mobility spectrum initially of the peptideGlu-Fibrinopeptide B and then subsequently of the fragments of thepeptide. The doubly protonated parent ion having a mass to charge ratioof 785.8 was initially arranged to be transmitted by a first quadrupolerod set mass filter 7 and was injected into a collision, fragmentationor reaction device 8 which comprised a collision cell. An energy voltageof 15V was applied to the collision cell. The ions were arranged toemerge from the collision cell and were passed to an ion mobilityspectrometer or separator 10. The ions were then temporally separatedaccording to their ion mobility in an ion mobility spectrometer orseparator 10. A 7 V potential hill travelling at 300 m/sec wasrepeatedly translated along the length of the ion mobility spectrometeror separator 10 in order to separate ions temporally. The ion mobilityspectrometer or separator 10 was maintained at a pressure of 0.2 mbar.The ions were detected with an ion detector 15. The peptide ion was thenfragmented. In order to fragment the peptide ion a potential differenceof 38 V was maintained so that ions were energetically accelerated inthe collision cell. An ion mobility spectrum of the resulting fragmentions is also shown in FIG. 5.

FIG. 6 shows a normal mass spectrum of the fragment ions resulting fromthe fragmentation of the doubly charged protonated ion of the peptideGlu-Fibrinopeptide B.

The upper curve of FIG. 7 shows an ion mobility spectrum for all of thefragment ions resulting from the fragmentation of the doubly charged ionof the peptide Glu-Fibrinopeptide B. The lower curve of FIG. 7 showsoverlapped ion mobility spectra for various specific fragment ions whichresulted from the fragmentation of the doubly charged ion of the samepeptide. The second quadrupole mass filter 16 was set to transmit ionshaving just the mass to charge ratios specified in order to generateeach individual ion mobility spectrum shown in FIG. 7. The duration ofthe ion mobility experiment was 12 ms and each individual ion mobilityspectrum was recorded over the full duration of the ion mobilityexperiment. It can be seen from this data that the second quadrupolemass filter 16 could be set so as to transmit several different fragmentor daughter ions at different stages or times during the course of anion mobility experiment.

The embodiment illustrated in FIG. 3 may also be used to conduct aparent or precursor ion scanning experiment. In a conventional massspectrometer the second quadrupole rod set mass filter would be set totransmit a specific characteristic fragment or daughter ion whilst thefirst quadrupole rod set mass filter would be scanned so as tosequentially transmit specific parent or precursor ions to a gascollision cell for fragmentation. When a specific fragment or daughterion is detected then the mass to charge ratio of the correspondingparent or precursor ion transmitted by the first quadrupole mass filterwould be recorded. This approach has proved particularly useful in theanalysis of protein post-translational modifications, such asphosphorylation and glycosylation. However, since it is necessary toscan the first quadrupole rod set mass filter the sampling duty cyclecan be quite low, commonly less than 1%. Consequently the sensitivity islow.

A mass spectrometer according to the embodiment shown in FIG. 3 can beoperated in a mode of operation wherein all the ions are transmittedthrough the first quadrupole rod set mass filter 7 and are received andaccumulated in the collision, fragmentation or reaction device 8 withoutbeing caused to fragment or react. The stored parent or precursor ionsare then preferably periodically released in a pulse from the collision,fragmentation or reaction device 8 and are then preferably temporallyseparated in the ion mobility spectrometer or separator 10. The parentor precursor ions are then preferably fragmented or reacted in the ionguide 13 arranged downstream of the ion mobility spectrometer orseparator 10 as the ions enter the ion guide 13. The resulting fragment,daughter, product or adduct ion are then preferably transmitted to thesecond mass filter 16 which is preferably arranged to transmit onlycertain specific fragment, daughter, product or adduct ions. Thisembodiment provides a means of parent or precursor ion scanning having aduty cycle of substantially 100%. It will be appreciated that this isparticularly advantageous compared to conventional arrangements whichexhibit a very low duty cycle, for example, when scanning a conventionaltriple quadrupole mass spectrometer.

Other embodiments of the present invention are also contemplated whereinthe AC or RF voltage supplied to electrodes forming the ion mobilityspectrometer or separator 10 and/or the ion guide 13 downstream of theion mobility spectrometer or separator 10 and/or the collision,fragmentation or reaction device 8 upstream of the ion mobilityspectrometer or separator 10 may comprise a non-sinusoidal voltage andmay, for example, comprise a square wave.

According to an embodiment the collision, fragmentation or reactiondevice 8, the ion mobility spectrometer or separator 10 and the ionguide 13 may comprise an ion tunnel ion guide i.e. a plurality ofelectrodes wherein each electrode has an aperture therein through whichions are transmitted. The electrodes preferably have substantiallysimilar sized apertures. The electrodes may comprise essentially asquare or rectangular plate or a ring. The apertures are preferablycircular. The collision, fragmentation or reaction device 8 and/or theion mobility spectrometer or separator 10 and/or the ion guide 13 maycomprise at least 10, 20, 30, 40, 50, 60, 70, 80, 90 or 100 electrodesof which at least 60%, 65%, 70%, 75%, 80%, 85%, 90% or 95% haveapertures which are substantially the same size or area.

Although the present invention has been described with reference topreferred embodiments, it will be understood by those skilled in the artthat various changes in form and detail may be made without departingfrom the scope of the invention as set forth in the accompanying claims.

The invention claimed is:
 1. A mass spectrometer comprising: an ionmobility spectrometer or separator for temporally separating parent orprecursor ions; a mass filter arranged downstream of said ion mobilityspectrometer or separator for mass filtering ions, wherein the massfilter is arranged and configured to transmit different ions atdifferent times; a collision, fragmentation or reaction device forfragmenting or reacting parent or precursor ions to produce fragment orproduct ions; and a mass analyser.
 2. A mass spectrometer as claimed inclaim 1, wherein the collision, fragmentation or reaction device isarranged downstream of said mass filter; and the mass analyser isarranged downstream of the collision, fragmentation or reaction devicefor mass analysing the fragment or product.
 3. A mass spectrometer asclaimed in claim 1, wherein said mass filter is scanned.
 4. A massspectrometer as claimed in claim 3, wherein said mass filter is scannedin synchronism with said ion mobility spectrometer or separator.
 5. Amass spectrometer as claimed in claim 1, wherein said mass filterselectively transmits different precursor ions at different times.
 6. Amass spectrometer as claimed in claim 5, wherein said mass filterselectively transmits multiple different precursor ions during a singleion mobility separation period.
 7. A mass spectrometer as claimed inclaim 1, wherein the mass filter selectively transmits parent orprecursor ions based on their drift times through the ion mobilityspectrometer or separator.
 8. A mass spectrometer as claimed in claim 1,wherein said mass analyser is a Time of Flight mass analyser.
 9. A massspectrometer as claimed in claim 1, wherein said collision,fragmentation or reaction device is arranged and adapted to fragmentions by Collision Induced Dissociation.
 10. A mass spectrometer asclaimed in claim 1, wherein said collision, fragmentation or reactiondevice is selected from the group consisting of: (i) a Surface InducedDissociation (“SID”) fragmentation device; (ii) an Electron TransferDissociation fragmentation device; (iii) an Electron CaptureDissociation fragmentation device; (iv) an Electron Collision or ImpactDissociation fragmentation device; (v) a Photo Induced Dissociation(“PID”) fragmentation device; (vi) a Laser Induced Dissociationfragmentation device; (vii) an infrared radiation induced dissociationdevice; (viii) an ultraviolet radiation induced dissociation device;(ix) a nozzle-skimmer interface fragmentation device; (x) an in-sourcefragmentation device; (xi) an ion-source Collision Induced Dissociationfragmentation device; (xii) a thermal or temperature sourcefragmentation device; (xiii) an electric field induced fragmentationdevice; (xiv) a magnetic field induced fragmentation device; (xv) anenzyme digestion or enzyme degradation fragmentation device; (xvi) anion-ion reaction fragmentation device; (xvii) an ion-molecule reactionfragmentation device; (xviii) an ion-atom reaction fragmentation device;(xix) an ion-metastable ion reaction fragmentation device; (xx) anion-metastable molecule reaction fragmentation device; (xxi) anion-metastable atom reaction fragmentation device; (xxii) an ion-ionreaction device for reacting ions to form adduct or product ions;(xxiii) an ion-molecule reaction device for reacting ions to form adductor product ions; (xxiv) an ion-atom reaction device for reacting ions toform adduct or product ions; (xxv) an ion-metastable ion reaction devicefor reacting ions to form adduct or product ions; (xxvi) anion-metastable molecule reaction device for reacting ions to form adductor product ions; and (xxvii) an ion-metastable atom reaction device forreacting ions to form adduct or product ions.
 11. A mass spectrometer asclaimed in claim 1, further comprising a voltage supply arranged andadapted to apply one or more voltages or potentials or one or morevoltage or potential waveforms to electrodes forming said collision,fragmentation or reaction device in order to urge at least some ionsalong the axial length of said collision, fragmentation or reactiondevice.
 12. A mass spectrometer as claimed in claim 1, furthercomprising a transient DC voltage supply arranged and adapted to applyone or more transient DC voltages or potentials or one or more transientDC voltage or potential waveforms to electrodes forming said collision,fragmentation or reaction device in order to urge at least some ionsalong the axial length of said collision, fragmentation or reactiondevice.
 13. A mass spectrometer as claimed in claim 1, furthercomprising AC or RF voltage means arranged and adapted to apply two ormore phase-shifted AC or RF voltages to electrodes forming saidcollision, fragmentation or reaction device in order to urge at leastsome ions along the axial length of said collision, fragmentation orreaction device.
 14. A mass spectrometer as claimed in claim 1, whereinsaid collision, fragmentation or reaction device is arranged and adaptedto retain or confine or partition ions emerging from said ion mobilityspectrometer or separator and to translate ions along the axial lengthof said collision, fragmentation or reaction device whilst substantiallymaintaining the order or fidelity in which ions emerge from said ionmobility spectrometer or separator.
 15. A mass spectrometer as claimedin claim 1, further comprising a control system arranged and adapted toswitch or repeatedly switch said collision, fragmentation or reactiondevice between a relatively high fragmentation or reaction mode ofoperation wherein ions are substantially fragmented or reacted and arelatively low fragmentation or reaction mode of operation whereinsubstantially fewer or no ions are fragmented or reacted in saidcollision, fragmentation or reaction device.
 16. A mass spectrometer asclaimed in claim 1, wherein said mass filter is a quadrupole rod setmass filter.
 17. A method of mass spectrometry comprising: temporallyseparating parent or precursor ions in an ion mobility spectrometer orseparator; mass filtering ions in a mass filter arranged downstream ofsaid ion mobility spectrometer or separator, wherein the mass filtertransmits different ions at different times; fragmenting or reactingparent or precursor ions in a collision, fragmentation or reactiondevice to produce fragment or product ions; and mass analysing saidfragment or product ions.